plucky (3) pcre2api.3.gz

Provided by: libpcre2-dev_10.45-1_amd64 bug

NAME

       PCRE2 - Perl-compatible regular expressions (revised API)

       #include <pcre2.h>

       PCRE2  is  a  new API for PCRE, starting at release 10.0. This document contains a description of all its
       native functions. See the pcre2 document for an overview of all the PCRE2 documentation.

PCRE2 NATIVE API BASIC FUNCTIONS

       pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
         uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
         pcre2_compile_context *ccontext);

       void pcre2_code_free(pcre2_code *code);

       pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
         pcre2_general_context *gcontext);

       pcre2_match_data *pcre2_match_data_create_from_pattern(
         const pcre2_code *code, pcre2_general_context *gcontext);

       int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext,
         int *workspace, PCRE2_SIZE wscount);

       void pcre2_match_data_free(pcre2_match_data *match_data);

PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS

       PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);

       PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);

       PCRE2_SIZE pcre2_get_match_data_heapframes_size(
         pcre2_match_data *match_data);

       uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

       PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

       PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS

       pcre2_general_context *pcre2_general_context_create(
         void *(*private_malloc)(PCRE2_SIZE, void *),
         void (*private_free)(void *, void *), void *memory_data);

       pcre2_general_context *pcre2_general_context_copy(
         pcre2_general_context *gcontext);

       void pcre2_general_context_free(pcre2_general_context *gcontext);

PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS

       pcre2_compile_context *pcre2_compile_context_create(
         pcre2_general_context *gcontext);

       pcre2_compile_context *pcre2_compile_context_copy(
         pcre2_compile_context *ccontext);

       void pcre2_compile_context_free(pcre2_compile_context *ccontext);

       int pcre2_set_bsr(pcre2_compile_context *ccontext,
         uint32_t value);

       int pcre2_set_character_tables(pcre2_compile_context *ccontext,
         const uint8_t *tables);

       int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
         uint32_t extra_options);

       int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
         PCRE2_SIZE value);

       int pcre2_set_max_pattern_compiled_length(
         pcre2_compile_context *ccontext, PCRE2_SIZE value);

       int pcre2_set_max_varlookbehind(pcre2_compile_contest *ccontext,
         uint32_t value);

       int pcre2_set_newline(pcre2_compile_context *ccontext,
         uint32_t value);

       int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
         uint32_t value);

       int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
         int (*guard_function)(uint32_t, void *), void *user_data);

       int pcre2_set_optimize(pcre2_compile_context *ccontext,
         uint32_t directive);

PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS

       pcre2_match_context *pcre2_match_context_create(
         pcre2_general_context *gcontext);

       pcre2_match_context *pcre2_match_context_copy(
         pcre2_match_context *mcontext);

       void pcre2_match_context_free(pcre2_match_context *mcontext);

       int pcre2_set_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_callout_block *, void *),
         void *callout_data);

       int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_substitute_callout_block *, void *),
         void *callout_data);

       int pcre2_set_substitute_case_callout(pcre2_match_context *mcontext,
         PCRE2_SIZE (*callout_function)(PCRE2_SPTR, PCRE2_SIZE,
                                        PCRE2_UCHAR *, PCRE2_SIZE,
                                        int, void *),
         void *callout_data);

       int pcre2_set_offset_limit(pcre2_match_context *mcontext,
         PCRE2_SIZE value);

       int pcre2_set_heap_limit(pcre2_match_context *mcontext,
         uint32_t value);

       int pcre2_set_match_limit(pcre2_match_context *mcontext,
         uint32_t value);

       int pcre2_set_depth_limit(pcre2_match_context *mcontext,
         uint32_t value);

PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS

       int pcre2_substring_copy_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);

       int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_UCHAR *buffer,
         PCRE2_SIZE *bufflen);

       void pcre2_substring_free(PCRE2_UCHAR *buffer);

       int pcre2_substring_get_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);

       int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_UCHAR **bufferptr,
         PCRE2_SIZE *bufflen);

       int pcre2_substring_length_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_SIZE *length);

       int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_SIZE *length);

       int pcre2_substring_nametable_scan(const pcre2_code *code,
         PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);

       int pcre2_substring_number_from_name(const pcre2_code *code,
         PCRE2_SPTR name);

       void pcre2_substring_list_free(PCRE2_UCHAR **list);

       int pcre2_substring_list_get(pcre2_match_data *match_data,
         PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);

PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION

       int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext, PCRE2_SPTR replacementz,
         PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
         PCRE2_SIZE *outlengthptr);

PCRE2 NATIVE API JIT FUNCTIONS

       int pcre2_jit_compile(pcre2_code *code, uint32_t options);

       int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

       pcre2_jit_stack *pcre2_jit_stack_create(size_t startsize,
         size_t maxsize, pcre2_general_context *gcontext);

       void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
         pcre2_jit_callback callback_function, void *callback_data);

       void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

PCRE2 NATIVE API SERIALIZATION FUNCTIONS

       int32_t pcre2_serialize_decode(pcre2_code **codes,
         int32_t number_of_codes, const uint8_t *bytes,
         pcre2_general_context *gcontext);

       int32_t pcre2_serialize_encode(const pcre2_code **codes,
         int32_t number_of_codes, uint8_t **serialized_bytes,
         PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);

       void pcre2_serialize_free(uint8_t *bytes);

       int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);

PCRE2 NATIVE API AUXILIARY FUNCTIONS

       pcre2_code *pcre2_code_copy(const pcre2_code *code);

       pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);

       int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
         PCRE2_SIZE bufflen);

       const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);

       void pcre2_maketables_free(pcre2_general_context *gcontext,
         const uint8_t *tables);

       int pcre2_pattern_info(const pcre2_code *code, uint32_t what,
         void *where);

       int pcre2_callout_enumerate(const pcre2_code *code,
         int (*callback)(pcre2_callout_enumerate_block *, void *),
         void *user_data);

       int pcre2_config(uint32_t what, void *where);

PCRE2 NATIVE API OBSOLETE FUNCTIONS

       int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
         uint32_t value);

       int pcre2_set_recursion_memory_management(
         pcre2_match_context *mcontext,
         void *(*private_malloc)(size_t, void *),
         void (*private_free)(void *, void *), void *memory_data);

       These functions became obsolete at release 10.30 and are retained only for backward  compatibility.  They
       should not be used in new code. The first is replaced by pcre2_set_depth_limit(); the second is no longer
       needed and has no effect (it always returns zero).

PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS

       pcre2_convert_context *pcre2_convert_context_create(
         pcre2_general_context *gcontext);

       pcre2_convert_context *pcre2_convert_context_copy(
         pcre2_convert_context *cvcontext);

       void pcre2_convert_context_free(pcre2_convert_context *cvcontext);

       int pcre2_set_glob_escape(pcre2_convert_context *cvcontext,
         uint32_t escape_char);

       int pcre2_set_glob_separator(pcre2_convert_context *cvcontext,
         uint32_t separator_char);

       int pcre2_pattern_convert(PCRE2_SPTR pattern, PCRE2_SIZE length,
         uint32_t options, PCRE2_UCHAR **buffer,
         PCRE2_SIZE *blength, pcre2_convert_context *cvcontext);

       void pcre2_converted_pattern_free(PCRE2_UCHAR *converted_pattern);

       These functions provide a way of converting non-PCRE2 patterns into patterns that  can  be  processed  by
       pcre2_compile(). This facility is experimental and may be changed in future releases. At present, "globs"
       and POSIX basic  and  extended  patterns  can  be  converted.  Details  are  given  in  the  pcre2convert
       documentation.

PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES

       There  are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit code units, respectively. However,
       there is just one header file, pcre2.h.  This contains the function prototypes and other definitions  for
       all  three  libraries.  One,  two, or all three can be installed simultaneously. On Unix-like systems the
       libraries are called libpcre2-8, libpcre2-16, and libpcre2-32,  and  they  can  also  co-exist  with  the
       original  PCRE libraries.  Every PCRE2 function comes in three different forms, one for each library, for
       example:

         pcre2_compile_8()
         pcre2_compile_16()
         pcre2_compile_32()

       There are also three different sets of data types:

         PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32
         PCRE2_SPTR8,  PCRE2_SPTR16,  PCRE2_SPTR32

       The UCHAR types define unsigned code units of the appropriate  widths.   For  example,  PCRE2_UCHAR16  is
       usually  defined  as `uint16_t'.  The SPTR types are pointers to constants of the equivalent UCHAR types,
       that is, they are pointers to vectors of unsigned code units.

       Character strings are passed to a PCRE2 library as sequences of unsigned integers in code  units  of  the
       appropriate  width.  The  length of a string may be given as a number of code units, or the string may be
       specified as zero-terminated.

       Many applications use only one code unit width. For their convenience, macros are defined whose names are
       the  generic  forms  such  as  pcre2_compile()  and  PCRE2_SPTR.  These macros use the value of the macro
       PCRE2_CODE_UNIT_WIDTH  to  generate  the   appropriate   width-specific   function   and   macro   names.
       PCRE2_CODE_UNIT_WIDTH  is not defined by default. An application must define it to be 8, 16, or 32 before
       including pcre2.h in order to make use of the generic names.

       Applications that use more than one code unit width can be linked with more than one PCRE2  library,  but
       must define PCRE2_CODE_UNIT_WIDTH to be 0 before including pcre2.h, and then use the real function names.
       Any code that is to be included in an environment where the value  of  PCRE2_CODE_UNIT_WIDTH  is  unknown
       should also use the real function names. (Unfortunately, it is not possible in C code to save and restore
       the value of a macro.)

       If PCRE2_CODE_UNIT_WIDTH is not defined before including pcre2.h, a compiler error occurs.

       When using multiple libraries in an application, you  must  take  care  when  processing  any  particular
       pattern  to  use  only  functions from a single library.  For example, if you want to run a match using a
       pattern  that  was  compiled  with  pcre2_compile_16(),  you  must  do  so  with  pcre2_match_16(),   not
       pcre2_match_8() or pcre2_match_32().

       In  the  function  summaries above, and in the rest of this document and other PCRE2 documents, functions
       and data types are described using their generic names, without the _8, _16, or _32 suffix.

PCRE2 API OVERVIEW

       PCRE2 has its own native API, which is described in this document. There are also some wrapper  functions
       for the 8-bit library that correspond to the POSIX regular expression API, but they do not give access to
       all the functionality of PCRE2 and they are  not  thread-safe.  They  are  described  in  the  pcre2posix
       documentation. Both these APIs define a set of C function calls.

       The  native  API  C  data  types,  function prototypes, option values, and error codes are defined in the
       header file pcre2.h, which also contains definitions of PCRE2_MAJOR and PCRE2_MINOR, the major and  minor
       release  numbers for the library. Applications can use these to include support for different releases of
       PCRE2.

       In a Windows environment, if you want to statically link an application program against a  non-dll  PCRE2
       library, you must define PCRE2_STATIC before including pcre2.h.

       The  functions  pcre2_compile() and pcre2_match() are used for compiling and matching regular expressions
       in a Perl-compatible manner. A sample program that  demonstrates  the  simplest  way  of  using  them  is
       provided  in  the  file called pcre2demo.c in the PCRE2 source distribution. A listing of this program is
       given in the pcre2demo documentation, and the pcre2sample documentation describes how to compile and  run
       it.

       The  compiling  and  matching  functions  recognize various options that are passed as bits in an options
       argument. There are also some more complicated parameters such as custom memory management functions  and
       resource  limits  that  are  passed in "contexts" (which are just memory blocks, described below). Simple
       applications do not need to make use of contexts.

       Just-in-time (JIT) compiler support is an optional feature of PCRE2 that  can  be  built  in  appropriate
       hardware  environments.  It  greatly  speeds  up  the matching performance of many patterns. Programs can
       request that it be used if available by calling pcre2_jit_compile() after a pattern has been successfully
       compiled by pcre2_compile(). This does nothing if JIT support is not available.

       More  complicated  programs  might need to make use of the specialist functions pcre2_jit_stack_create(),
       pcre2_jit_stack_free(), and pcre2_jit_stack_assign() in order to control the JIT code's memory usage.

       JIT matching is automatically used by pcre2_match() if it is available, unless the PCRE2_NO_JIT option is
       set.  There  is also a direct interface for JIT matching, which gives improved performance at the expense
       of less sanity checking. The JIT-specific functions are discussed in the pcre2jit documentation.

       A second matching function, pcre2_dfa_match(), which is not Perl-compatible, is also provided. This  uses
       a  different algorithm for the matching. The alternative algorithm finds all possible matches (at a given
       point in the subject), and scans the subject just once (unless there are lookaround assertions). However,
       this  algorithm  does  not  return  captured substrings. A description of the two matching algorithms and
       their advantages and disadvantages is given in the pcre2matching documentation. There is no  JIT  support
       for pcre2_dfa_match().

       In  addition to the main compiling and matching functions, there are convenience functions for extracting
       captured substrings from a subject string that has been matched by pcre2_match(). They are:

         pcre2_substring_copy_byname()
         pcre2_substring_copy_bynumber()
         pcre2_substring_get_byname()
         pcre2_substring_get_bynumber()
         pcre2_substring_list_get()
         pcre2_substring_length_byname()
         pcre2_substring_length_bynumber()
         pcre2_substring_nametable_scan()
         pcre2_substring_number_from_name()

       pcre2_substring_free() and pcre2_substring_list_free()  are  also  provided,  to  free  memory  used  for
       extracted  strings.  If  either  of  these functions is called with a NULL argument, the function returns
       immediately without doing anything.

       The function pcre2_substitute() can be called to match a pattern and return a copy of the subject  string
       with substitutions for parts that were matched.

       Functions  whose  names  begin  with  pcre2_serialize_  are  used for saving compiled patterns on disc or
       elsewhere, and reloading them later.

       Finally, there are functions for finding out information about a compiled pattern  (pcre2_pattern_info())
       and about the configuration with which PCRE2 was built (pcre2_config()).

       Functions  with  names  ending  with  _free() are used for freeing memory blocks of various sorts. In all
       cases, if one of these functions is called with a NULL argument, it does nothing.

STRING LENGTHS AND OFFSETS

       The PCRE2 API uses string lengths and offsets into strings of code units in several places. These  values
       are always of type PCRE2_SIZE, which is an unsigned integer type, currently always defined as size_t. The
       largest value that can be stored in such a type  (that  is  ~(PCRE2_SIZE)0)  is  reserved  as  a  special
       indicator  for  zero-terminated  strings  and  unset  offsets.  Therefore, the longest string that can be
       handled is one less than this maximum. Note that string lengths are always given in code units.  Only  in
       the 8-bit library is such a length the same as the number of bytes in the string.

NEWLINES

       PCRE2  supports  five  different conventions for indicating line breaks in strings: a single CR (carriage
       return) character, a single LF (linefeed) character, the two-character sequence CRLF, any  of  the  three
       preceding,  or  any Unicode newline sequence. The Unicode newline sequences are the three just mentioned,
       plus the single characters VT (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS
       (line separator, U+2028), and PS (paragraph separator, U+2029).

       Each  of  the  first  three  conventions is used by at least one operating system as its standard newline
       sequence. When PCRE2 is built, a default can be specified.  If it is not, the default is set to LF, which
       is  the  Unix  standard.  However,  the  newline convention can be changed by an application when calling
       pcre2_compile(), or it can be specified by special  text  at  the  start  of  the  pattern  itself;  this
       overrides any other settings. See the pcre2pattern page for details of the special character sequences.

       In  the  PCRE2 documentation the word "newline" is used to mean "the character or pair of characters that
       indicate a line break". The choice of newline convention affects the handling of the dot, circumflex, and
       dollar  metacharacters, the handling of #-comments in /x mode, and, when CRLF is a recognized line ending
       sequence, the match position advancement for a non-anchored pattern. There is more detail about  this  in
       the section on pcre2_match() options below.

       The choice of newline convention does not affect the interpretation of the \n or \r escape sequences, nor
       does it affect what \R matches; this has its own separate convention.

MULTITHREADING

       In a multithreaded application it is important to keep thread-specific data separate from data  that  can
       be  shared between threads. The PCRE2 library code itself is thread-safe: it contains no static or global
       variables. The API is designed to be fairly simple for non-threaded applications while at the  same  time
       ensuring that multithreaded applications can use it.

       There  are several different blocks of data that are used to pass information between the application and
       the PCRE2 libraries.

   The compiled pattern

       A pointer to the compiled form of a pattern is returned to the user when pcre2_compile()  is  successful.
       The data in the compiled pattern is fixed, and does not change when the pattern is matched. Therefore, it
       is thread-safe, that is, the same compiled pattern can be used by more than  one  thread  simultaneously.
       For  example,  an  application  can  compile  all  its patterns at the start, before forking off multiple
       threads that use them. However, if the just-in-time (JIT) optimization feature is being  used,  it  needs
       separate memory stack areas for each thread. See the pcre2jit documentation for more details.

       In  a  more  complicated  situation, where patterns are compiled only when they are first needed, but are
       still shared between threads, pointers to compiled patterns must be protected from  simultaneous  writing
       by  multiple  threads.  This is somewhat tricky to do correctly. If you know that writing to a pointer is
       atomic in your environment, you can use logic like this:

         Get a read-only (shared) lock (mutex) for pointer
         if (pointer == NULL)
           {
           Get a write (unique) lock for pointer
           if (pointer == NULL) pointer = pcre2_compile(...
           }
         Release the lock
         Use pointer in pcre2_match()

       Of course, testing for compilation errors should also be included in the code.

       The reason for checking the pointer a second time is as follows: Several threads may  have  acquired  the
       shared  lock  and  tested  the pointer for being NULL, but only one of them will be given the write lock,
       with the rest kept waiting. The winning thread will compile the pattern and store the result.  After this
       thread  releases  the write lock, another thread will get it, and if it does not retest pointer for being
       NULL, will recompile the pattern and overwrite the pointer, creating a memory leak and  possibly  causing
       other issues.

       In  an  environment  where writing to a pointer may not be atomic, the above logic is not sufficient. The
       thread that is doing the compiling may be descheduled after writing only part of the pointer, which could
       cause  other threads to use an invalid value. Instead of checking the pointer itself, a separate "pointer
       is valid" flag (that can be updated atomically) must be used:

         Get a read-only (shared) lock (mutex) for pointer
         if (!pointer_is_valid)
           {
           Get a write (unique) lock for pointer
           if (!pointer_is_valid)
             {
             pointer = pcre2_compile(...
             pointer_is_valid = TRUE
             }
           }
         Release the lock
         Use pointer in pcre2_match()

       If JIT is being used, but the JIT compilation is not being done immediately (perhaps waiting  to  see  if
       the  pattern is used often enough), similar logic is required. JIT compilation updates a value within the
       compiled code block,  so  a  thread  must  gain  unique  write  access  to  the  pointer  before  calling
       pcre2_jit_compile().  Alternatively,  pcre2_code_copy()  or  pcre2_code_copy_with_tables() can be used to
       obtain a private copy of the compiled code before calling the JIT compiler.

   Context blocks

       The next main section below introduces the idea of "contexts" in which  PCRE2  functions  are  called.  A
       context  is  nothing more than a collection of parameters that control the way PCRE2 operates. Grouping a
       number of parameters together in a context is a convenient way  of  passing  them  to  a  PCRE2  function
       without  using  lots of arguments. The parameters that are stored in contexts are in some sense "advanced
       features" of the API. Many straightforward applications will not need to use contexts.

       In a multithreaded application, if the parameters in a context are values that  are  never  changed,  the
       same  context  can  be  used  by  all  the threads. However, if any thread needs to change any value in a
       context, it must make its own thread-specific copy.

   Match blocks

       The matching functions need a block of memory for storing the results of a match. This  includes  details
       of what was matched, as well as additional information such as the name of a (*MARK) setting. Each thread
       must provide its own copy of this memory.

PCRE2 CONTEXTS

       Some PCRE2 functions have a lot of parameters, many of which are used only  by  specialist  applications,
       for  example,  those that use custom memory management or non-standard character tables. To keep function
       argument lists at a reasonable size, and at  the  same  time  to  keep  the  API  extensible,  "uncommon"
       parameters are passed to certain functions in a context instead of directly. A context is just a block of
       memory that holds the parameter values.  Applications that do not need  to  adjust  any  of  the  context
       parameters can pass NULL when a context pointer is required.

       There  are  three  different  types  of  context:  a  general  context that is relevant for several PCRE2
       operations, a compile-time context, and a match-time context.

   The general context

       At present, this context just contains pointers to (and data for) external  memory  management  functions
       that  are  called  from  several  places in the PCRE2 library. The context is named `general' rather than
       specifically `memory' because in future other fields may be added. If you do not want to supply your  own
       custom  memory  management functions, you do not need to bother with a general context. A general context
       is created by:

       pcre2_general_context *pcre2_general_context_create(
         void *(*private_malloc)(PCRE2_SIZE, void *),
         void (*private_free)(void *, void *), void *memory_data);

       The two function pointers specify custom memory management functions, whose prototypes are:

         void *private_malloc(PCRE2_SIZE, void *);
         void  private_free(void *, void *);

       Whenever code in PCRE2 calls these functions, the final argument is the value of memory_data.  Either  of
       the  first two arguments of the creation function may be NULL, in which case the system memory management
       functions malloc() and free() are used. (This is not currently useful, as there are no other fields in  a
       general  context,  but in future there might be.)  The private_malloc() function is used (if supplied) to
       obtain memory for storing the context, and all three values are saved as part of the context.

       Whenever PCRE2 creates a data block of any kind, the block contains a pointer to the free() function that
       matches  the  malloc()  function  that  was used. When the time comes to free the block, this function is
       called.

       A general context can be copied by calling:

       pcre2_general_context *pcre2_general_context_copy(
         pcre2_general_context *gcontext);

       The memory used for a general context should be freed by calling:

       void pcre2_general_context_free(pcre2_general_context *gcontext);

       If this function is passed a NULL argument, it returns immediately without doing anything.

   The compile context

       A compile context is required if you want to provide an  external  function  for  stack  checking  during
       compilation or to change the default values of any of the following compile-time parameters:

         What \R matches (Unicode newlines or CR, LF, CRLF only)
         PCRE2's character tables
         The newline character sequence
         The compile time nested parentheses limit
         The maximum length of the pattern string
         The extra options bits (none set by default)
         Which performance optimizations the compiler should apply

       A  compile  context  is also required if you are using custom memory management.  If none of these apply,
       just pass NULL as the context argument of pcre2_compile().

       A compile context is created, copied, and freed by the following functions:

       pcre2_compile_context *pcre2_compile_context_create(
         pcre2_general_context *gcontext);

       pcre2_compile_context *pcre2_compile_context_copy(
         pcre2_compile_context *ccontext);

       void pcre2_compile_context_free(pcre2_compile_context *ccontext);

       A compile context is created with default values for its parameters. These can be changed by calling  the
       following functions, which return 0 on success, or PCRE2_ERROR_BADDATA if invalid data is detected.

       int pcre2_set_bsr(pcre2_compile_context *ccontext,
         uint32_t value);

       The   value   must  be  PCRE2_BSR_ANYCRLF,  to  specify  that  \R  matches  only  CR,  LF,  or  CRLF,  or
       PCRE2_BSR_UNICODE, to specify that \R matches any Unicode line ending sequence. The value is used by  the
       JIT compiler and by the two interpreted matching functions, pcre2_match() and pcre2_dfa_match().

       int pcre2_set_character_tables(pcre2_compile_context *ccontext,
         const uint8_t *tables);

       The  value  must be the result of a call to pcre2_maketables(), whose only argument is a general context.
       This function builds a set of character tables in the current locale.

       int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
         uint32_t extra_options);

       As PCRE2 has developed, almost all the 32 option bits that are  available  in  the  options  argument  of
       pcre2_compile()  have  been  used  up.  To avoid running out, the compile context contains a set of extra
       option bits which are used for some newer, assumed rarer, options. This  function  sets  those  bits.  It
       always  sets  all  the  bits  (either  on or off). It does not modify any existing setting. The available
       options are defined in the section entitled "Extra compile options" below.

       int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
         PCRE2_SIZE value);

       This sets a maximum length, in code units, for any pattern string that is compiled with this context.  If
       the pattern is longer, an error is generated.  This facility is provided so that applications that accept
       patterns from external sources can limit their size. The default is the largest number that a  PCRE2_SIZE
       variable can hold, which is effectively unlimited.

       int pcre2_set_max_pattern_compiled_length(
         pcre2_compile_context *ccontext, PCRE2_SIZE value);

       This  sets a maximum size, in bytes, for the memory needed to hold the compiled version of a pattern that
       is compiled with this context. If the pattern needs more memory, an error is generated. This facility  is
       provided  so  that applications that accept patterns from external sources can limit the amount of memory
       they use. The default is the largest number that a PCRE2_SIZE variable can  hold,  which  is  effectively
       unlimited.

       int pcre2_set_max_varlookbehind(pcre2_compile_contest *ccontext,
         uint32_t value);

       This  sets  a  maximum  length  for  the  number  of  characters  matched by a variable-length lookbehind
       assertion. The default is set when PCRE2 is built, with the ultimate default being 255, the same as Perl.
       Lookbehind assertions without a bounding length are not supported.

       int pcre2_set_newline(pcre2_compile_context *ccontext,
         uint32_t value);

       This  specifies  which characters or character sequences are to be recognized as newlines. The value must
       be one of PCRE2_NEWLINE_CR (carriage return only), PCRE2_NEWLINE_LF (linefeed  only),  PCRE2_NEWLINE_CRLF
       (the   two-character   sequence   CR   followed   by  LF),  PCRE2_NEWLINE_ANYCRLF  (any  of  the  above),
       PCRE2_NEWLINE_ANY (any Unicode newline sequence), or PCRE2_NEWLINE_NUL (the  NUL  character,  that  is  a
       binary zero).

       A  pattern can override the value set in the compile context by starting with a sequence such as (*CRLF).
       See the pcre2pattern page for details.

       When a pattern is compiled with the PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option, the newline  convention
       affects  the  recognition  of  the  end of internal comments starting with #. The value is saved with the
       compiled pattern for subsequent use by the JIT compiler and by the two  interpreted  matching  functions,
       pcre2_match() and pcre2_dfa_match().

       int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
         uint32_t value);

       This  parameter  adjusts  the  limit,  set when PCRE2 is built (default 250), on the depth of parenthesis
       nesting in a pattern. This limit stops rogue patterns using up too much system stack when being compiled.
       The limit applies to parentheses of all kinds, not just capturing parentheses.

       int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
         int (*guard_function)(uint32_t, void *), void *user_data);

       There  is  at  least  one  application  that  runs PCRE2 in threads with very limited system stack, where
       running out of stack is to be avoided at all costs. The parenthesis limit above cannot  take  account  of
       how  much  stack is actually available during compilation. For a finer control, you can supply a function
       that is called whenever pcre2_compile() starts to  compile  a  parenthesized  part  of  a  pattern.  This
       function can check the actual stack size (or anything else that it wants to, of course).

       The  first  argument  to  the callout function gives the current depth of nesting, and the second is user
       data that is set up by the last argument of  pcre2_set_compile_recursion_guard().  The  callout  function
       should return zero if all is well, or non-zero to force an error.

       int pcre2_set_optimize(pcre2_compile_context *ccontext,
         uint32_t directive);

       PCRE2  can  apply various performance optimizations during compilation, in order to make matching faster.
       For example, the compiler might  convert  some  regex  constructs  into  an  equivalent  construct  which
       pcre2_match()  can  execute faster. By default, all available optimizations are enabled. However, in rare
       cases, one might wish to  disable  specific  optimizations.  For  example,  if  it  is  known  that  some
       optimizations cannot benefit a certain regex, it might be desirable to disable them, in order to speed up
       compilation.

       The permitted values of directive are as follows:

         PCRE2_OPTIMIZATION_FULL

       Enable all optional performance optimizations. This is the default value.

         PCRE2_OPTIMIZATION_NONE

       Disable all optional performance optimizations.

         PCRE2_AUTO_POSSESS
         PCRE2_AUTO_POSSESS_OFF

       Enable/disable "auto-possessification" of variable quantifiers such as * and +.  This  optimization,  for
       example,  turns a+b into a++b in order to avoid backtracks into a+ that can never be successful. However,
       if callouts are in use, auto-possessification means that some callouts are never taken. You  can  disable
       this  optimization  if  you  want the matching functions to do a full, unoptimized search and run all the
       callouts.

         PCRE2_DOTSTAR_ANCHOR
         PCRE2_DOTSTAR_ANCHOR_OFF

       Enable/disable an optimization that is applied when .* is the  first  significant  item  in  a  top-level
       branch  of a pattern, and all the other branches also start with .* or with \A or \G or ^. Such a pattern
       is automatically anchored if PCRE2_DOTALL is set for all the .* items and PCRE2_MULTILINE is not set  for
       any  ^  items.  Otherwise,  the  fact  that  any  match  must start either at the start of the subject or
       following a newline is remembered. Like other optimizations, this can cause callouts to be skipped.

       Dotstar anchor optimization is automatically disabled for .* if it is inside an atomic group or a capture
       group that is the subject of a backreference, or if the pattern contains (*PRUNE) or (*SKIP).

         PCRE2_START_OPTIMIZE
         PCRE2_START_OPTIMIZE_OFF

       Enable/disable  optimizations which cause matching functions to scan the subject string for specific code
       unit values before attempting a match. For example, if it is known that an unanchored  match  must  start
       with a specific value, the matching code searches the subject for that value, and fails immediately if it
       cannot find it, without actually running the main matching function. This means that a special item  such
       as  (*COMMIT)  at  the start of a pattern is not considered until after a suitable starting point for the
       match has been found.  Also, when callouts or (*MARK) items are in use,  these  "start-up"  optimizations
       can  cause  them  to  be skipped if the pattern is never actually used. The start-up optimizations are in
       effect a pre-scan of the subject that takes place before the pattern is run.

       Disabling start-up optimizations ensures that in cases where the result is "no match",  the  callouts  do
       occur, and that items such as (*COMMIT) and (*MARK) are considered at every possible starting position in
       the subject string.

       Disabling start-up optimizations may change the outcome of a matching operation.  Consider the pattern

         (*COMMIT)ABC

       When this is compiled, PCRE2 records the fact that a match must start with the character "A". Suppose the
       subject  string  is  "DEFABC".  The start-up optimization scans along the subject, finds "A" and runs the
       first match attempt from there. The (*COMMIT) item means that the pattern must match the current starting
       position,  which in this case, it does. However, if the same match is run without start-up optimizations,
       the initial scan along the subject string does not happen. The first match attempt is run  starting  from
       "D" and when this fails, (*COMMIT) prevents any further matches being tried, so the overall result is "no
       match".

       Another start-up optimization makes use of a minimum length for a matching  subject,  which  is  recorded
       when possible. Consider the pattern

         (*MARK:1)B(*MARK:2)(X|Y)

       The  minimum  length  for  a  match is two characters. If the subject is "XXBB", the "starting character"
       optimization skips "XX", then tries to match "BB", which is long enough. In  the  process,  (*MARK:2)  is
       encountered  and  remembered.  When the match attempt fails, the next "B" is found, but there is only one
       character left, so there are no more attempts, and "no match" is returned with the "last mark  seen"  set
       to  "2".  Without start-up optimizations, however, matches are tried at every possible starting position,
       including at the end of the subject, where (*MARK:1) is encountered, but there is no "B",  so  the  "last
       mark  seen"  that  is  returned  is  "1". In this case, the optimizations do not affect the overall match
       result, which is still "no match", but they do affect the auxiliary information that is returned.

   The match context

       A match context is required if you want to:

         Set up a callout function
         Set an offset limit for matching an unanchored pattern
         Change the limit on the amount of heap used when matching
         Change the backtracking match limit
         Change the backtracking depth limit
         Set custom memory management specifically for the match

       If none of these apply, just pass NULL as the context argument of  pcre2_match(),  pcre2_dfa_match(),  or
       pcre2_jit_match().

       A match context is created, copied, and freed by the following functions:

       pcre2_match_context *pcre2_match_context_create(
         pcre2_general_context *gcontext);

       pcre2_match_context *pcre2_match_context_copy(
         pcre2_match_context *mcontext);

       void pcre2_match_context_free(pcre2_match_context *mcontext);

       A  match  context  is created with default values for its parameters. These can be changed by calling the
       following functions, which return 0 on success, or PCRE2_ERROR_BADDATA if invalid data is detected.

       int pcre2_set_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_callout_block *, void *),
         void *callout_data);

       This sets up a callout function for PCRE2 to call  at  specified  points  during  a  matching  operation.
       Details are given in the pcre2callout documentation.

       int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_substitute_callout_block *, void *),
         void *callout_data);

       This  sets  up  a  callout function for PCRE2 to call after each substitution made by pcre2_substitute().
       Details are given in the section entitled "Creating a new string with substitutions" below.

       int pcre2_set_substitute_case_callout(pcre2_match_context *mcontext,
         PCRE2_SIZE (*callout_function)(PCRE2_SPTR, PCRE2_SIZE,
                                        PCRE2_UCHAR *, PCRE2_SIZE,
                                        int, void *),
         void *callout_data);

       This sets up  a  callout  function  for  PCRE2  to  call  when  performing  case  transformations  inside
       pcre2_substitute().  Details are given in the section entitled "Creating a new string with substitutions"
       below.

       int pcre2_set_offset_limit(pcre2_match_context *mcontext,
         PCRE2_SIZE value);

       The offset_limit parameter limits how far an unanchored search can advance in  the  subject  string.  The
       default    value   is   PCRE2_UNSET.   The   pcre2_match()   and   pcre2_dfa_match()   functions   return
       PCRE2_ERROR_NOMATCH if a match with a starting point before or at the given  offset  is  not  found.  The
       pcre2_substitute() function makes no more substitutions.

       For  example,  if  the  pattern  /abc/  is matched against "123abc" with an offset limit less than 3, the
       result is PCRE2_ERROR_NOMATCH. A match can never be found if the startoffset argument  of  pcre2_match(),
       pcre2_dfa_match(), or pcre2_substitute() is greater than the offset limit set in the match context.

       When  using this facility, you must set the PCRE2_USE_OFFSET_LIMIT option when calling pcre2_compile() so
       that when JIT is in use, different code can be compiled. If a match is started with a  non-default  match
       limit when PCRE2_USE_OFFSET_LIMIT is not set, an error is generated.

       The  offset limit facility can be used to track progress when searching large subject strings or to limit
       the extent of global substitutions. See also the PCRE2_FIRSTLINE option, which requires a match to  start
       before  or at the first newline that follows the start of matching in the subject. If this is set with an
       offset limit, a match must occur in the first line and also within the  offset  limit.  In  other  words,
       whichever limit comes first is used.

       int pcre2_set_heap_limit(pcre2_match_context *mcontext,
         uint32_t value);

       The heap_limit parameter specifies, in units of kibibytes (1024 bytes), the maximum amount of heap memory
       that pcre2_match() may use to hold backtracking information when  running  an  interpretive  match.  This
       limit  also  applies  to pcre2_dfa_match(), which may use the heap when processing patterns with a lot of
       nested pattern recursion or lookarounds or atomic groups. This limit does not apply to matching with  the
       JIT  optimization, which has its own memory control arrangements (see the pcre2jit documentation for more
       details). If the limit is reached, the negative error code PCRE2_ERROR_HEAPLIMIT is returned. The default
       limit  can  be  set  when  PCRE2 is built; if it is not, the default is set very large and is essentially
       unlimited.

       A value for the heap limit may also be supplied by an item at the start of a pattern of the form

         (*LIMIT_HEAP=ddd)

       where ddd is a decimal number. However, such a setting is ignored unless ddd is less than the  limit  set
       by the caller of pcre2_match() or, if no such limit is set, less than the default.

       The  pcre2_match()  function always needs some heap memory, so setting a value of zero guarantees a "heap
       limit exceeded" error. Details of  how  pcre2_match()  uses  the  heap  are  given  in  the  pcre2perform
       documentation.

       For  pcre2_dfa_match(),  a  vector  on  the  system  stack  is  used  when processing pattern recursions,
       lookarounds, or atomic groups, and only if this is not big enough is heap  memory  used.  In  this  case,
       setting a value of zero disables the use of the heap.

       int pcre2_set_match_limit(pcre2_match_context *mcontext,
         uint32_t value);

       The match_limit parameter provides a means of preventing PCRE2 from using up too many computing resources
       when processing patterns that are not going to match, but which have a very large number of possibilities
       in their search trees. The classic example is a pattern that uses nested unlimited repeats.

       There is an internal counter in pcre2_match() that is incremented each time round its main matching loop.
       If this value reaches the match limit, pcre2_match() returns the negative  value  PCRE2_ERROR_MATCHLIMIT.
       This has the effect of limiting the amount of backtracking that can take place. For patterns that are not
       anchored, the count restarts from zero for each position in the subject string. This limit  also  applies
       to pcre2_dfa_match(), though the counting is done in a different way.

       When  pcre2_match()  is called with a pattern that was successfully processed by pcre2_jit_compile(), the
       way in which matching is executed is entirely different. However,  there  is  still  the  possibility  of
       runaway  matching  that  goes  on for a very long time, and so the match_limit value is also used in this
       case (but in a different way) to limit how long the matching can continue.

       The default value for the limit can be set when PCRE2 is built; the default is 10 million, which  handles
       all  but the most extreme cases. A value for the match limit may also be supplied by an item at the start
       of a pattern of the form

         (*LIMIT_MATCH=ddd)

       where ddd is a decimal number. However, such a setting is ignored unless ddd is less than the  limit  set
       by the caller of pcre2_match() or pcre2_dfa_match() or, if no such limit is set, less than the default.

       int pcre2_set_depth_limit(pcre2_match_context *mcontext,
         uint32_t value);

       This parameter limits the depth of nested backtracking in pcre2_match().  Each time a nested backtracking
       point is passed, a new memory frame is used to remember the state of matching at that point.  Thus,  this
       parameter  indirectly  limits  the amount of memory that is used in a match. However, because the size of
       each memory frame depends on the number of capturing parentheses, the actual  memory  limit  varies  from
       pattern  to  pattern.  This  limit was more useful in versions before 10.30, where function recursion was
       used for backtracking.

       The depth limit is not relevant, and is ignored, when matching is done using JIT compiled code.  However,
       it  is  supported  by  pcre2_dfa_match(),  which  uses it to limit the depth of nested internal recursive
       function calls that implement atomic groups, lookaround assertions, and pattern recursions. This  limits,
       indirectly,  the  amount  of system stack that is used. It was more useful in versions before 10.32, when
       stack memory was used for local workspace vectors for recursive function calls. From version 10.32,  only
       local  variables  are allocated on the stack and as each call uses only a few hundred bytes, even a small
       stack can support quite a lot of recursion.

       If the depth of internal recursive function calls is great enough, local workspace vectors are  allocated
       on  the  heap  from  version  10.32 onwards, so the depth limit also indirectly limits the amount of heap
       memory that is used. A recursive pattern such as /(.(?2))((?1)|)/, when matched to  a  very  long  string
       using  pcre2_dfa_match(),  can  use  a great deal of memory. However, it is probably better to limit heap
       usage directly by calling pcre2_set_heap_limit().

       The default value for the depth limit can be set when PCRE2 is built; if it is not, the default is set to
       the  same  value  as  the  default  for  the  match  limit.   If  the limit is exceeded, pcre2_match() or
       pcre2_dfa_match() returns PCRE2_ERROR_DEPTHLIMIT. A value for the depth limit may also be supplied by  an
       item at the start of a pattern of the form

         (*LIMIT_DEPTH=ddd)

       where  ddd  is a decimal number. However, such a setting is ignored unless ddd is less than the limit set
       by the caller of pcre2_match() or pcre2_dfa_match() or, if no such limit is set, less than the default.

CHECKING BUILD-TIME OPTIONS

       int pcre2_config(uint32_t what, void *where);

       The function pcre2_config() makes  it  possible  for  a  PCRE2  client  to  find  the  value  of  certain
       configuration  parameters  and  to  discover  which  optional  features have been compiled into the PCRE2
       library. The pcre2build documentation has more details about these features.

       The first argument for pcre2_config() specifies which information is required. The second argument  is  a
       pointer  to  memory  into  which  the  information is placed. If NULL is passed, the function returns the
       amount of memory that is needed for the requested information. For calls that  return  numerical  values,
       the  value is in bytes; when requesting these values, where should point to appropriately aligned memory.
       For calls that return strings, the required length is given in code units, not counting  the  terminating
       zero.

       When  requesting  information,  the returned value from pcre2_config() is non-negative on success, or the
       negative error code PCRE2_ERROR_BADOPTION if the value in the  first  argument  is  not  recognized.  The
       following information is available:

         PCRE2_CONFIG_BSR

       The  output  is  a uint32_t integer whose value indicates what character sequences the \R escape sequence
       matches by default. A value of PCRE2_BSR_UNICODE means that \R matches any Unicode line ending  sequence;
       a  value  of  PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF. The default can be overridden
       when a pattern is compiled.

         PCRE2_CONFIG_COMPILED_WIDTHS

       The output is a uint32_t integer whose lower bits indicate which code  unit  widths  were  selected  when
       PCRE2  was  built.  The 1-bit indicates 8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit
       support, respectively.

         PCRE2_CONFIG_DEPTHLIMIT

       The output is a uint32_t integer that gives the default limit for the depth  of  nested  backtracking  in
       pcre2_match()  or  the  depth  of nested recursions, lookarounds, and atomic groups in pcre2_dfa_match().
       Further details are given with pcre2_set_depth_limit() above.

         PCRE2_CONFIG_HEAPLIMIT

       The output is a uint32_t integer that gives, in kibibytes, the default  limit  for  the  amount  of  heap
       memory  used by pcre2_match() or pcre2_dfa_match(). Further details are given with pcre2_set_heap_limit()
       above.

         PCRE2_CONFIG_JIT

       The output is a uint32_t integer that is set to one if support for just-in-time compiling is included  in
       the  library; otherwise it is set to zero. Note that having the support in the library does not guarantee
       that JIT will be used for any given match, and neither does it guarantee that JIT will actually  be  able
       to  function,  because  it may not be able to allocate executable memory in some environments. There is a
       special call to pcre2_jit_compile() that can be used to check this. See the  pcre2jit  documentation  for
       more details.

         PCRE2_CONFIG_JITTARGET

       The  where  argument  should  point  to  a  buffer that is at least 48 code units long. (The exact length
       required can be found by calling pcre2_config() with where set to NULL.) The  buffer  is  filled  with  a
       string  that  contains the name of the architecture for which the JIT compiler is configured, for example
       "x86 32bit (little endian + unaligned)". If  JIT  support  is  not  available,  PCRE2_ERROR_BADOPTION  is
       returned, otherwise the number of code units used is returned. This is the length of the string, plus one
       unit for the terminating zero.

         PCRE2_CONFIG_LINKSIZE

       The output is a uint32_t integer that contains the number of bytes used for internal linkage in  compiled
       regular expressions. When PCRE2 is configured, the value can be set to 2, 3, or 4, with the default being
       2. This is the value that is returned by pcre2_config(). However, when the 16-bit library is compiled,  a
       value  of  3  is rounded up to 4, and when the 32-bit library is compiled, internal linkages always use 4
       bytes, so the configured value is not relevant.

       The default value of 2 for the 8-bit and 16-bit libraries is sufficient for  all  but  the  most  massive
       patterns,  since  it  allows the size of the compiled pattern to be up to 65535 code units. Larger values
       allow larger regular expressions to be compiled by those two libraries, but  at  the  expense  of  slower
       matching.

         PCRE2_CONFIG_MATCHLIMIT

       The  output  is  a uint32_t integer that gives the default match limit for pcre2_match(). Further details
       are given with pcre2_set_match_limit() above.

         PCRE2_CONFIG_NEWLINE

       The output is a uint32_t integer whose value specifies the default character sequence that is  recognized
       as meaning "newline". The values are:

         PCRE2_NEWLINE_CR       Carriage return (CR)
         PCRE2_NEWLINE_LF       Linefeed (LF)
         PCRE2_NEWLINE_CRLF     Carriage return, linefeed (CRLF)
         PCRE2_NEWLINE_ANY      Any Unicode line ending
         PCRE2_NEWLINE_ANYCRLF  Any of CR, LF, or CRLF
         PCRE2_NEWLINE_NUL      The NUL character (binary zero)

       The default should normally correspond to the standard sequence for your operating system.

         PCRE2_CONFIG_NEVER_BACKSLASH_C

       The  output is a uint32_t integer that is set to one if the use of \C was permanently disabled when PCRE2
       was built; otherwise it is set to zero.

         PCRE2_CONFIG_PARENSLIMIT

       The output is a uint32_t integer that gives the maximum depth of nesting of parentheses (of any kind)  in
       a pattern. This limit is imposed to cap the amount of system stack used when a pattern is compiled. It is
       specified when PCRE2 is built; the default is 250. This limit does not take into account the  stack  that
       may  already  be  used  by  the  calling application. For finer control over compilation stack usage, see
       pcre2_set_compile_recursion_guard().

         PCRE2_CONFIG_STACKRECURSE

       This parameter is obsolete and should not be used in new code. The output is a uint32_t integer  that  is
       always set to zero.

         PCRE2_CONFIG_TABLES_LENGTH

       The  output  is a uint32_t integer that gives the length of PCRE2's character processing tables in bytes.
       For details of these tables see the section on locale support below.

         PCRE2_CONFIG_UNICODE_VERSION

       The where argument should point to a buffer that is at least  24  code  units  long.  (The  exact  length
       required  can  be  found  by  calling  pcre2_config() with where set to NULL.) If PCRE2 has been compiled
       without Unicode support, the buffer is filled with the  text  "Unicode  not  supported".  Otherwise,  the
       Unicode  version  string  (for  example, "8.0.0") is inserted. The number of code units used is returned.
       This is the length of the string plus one unit for the terminating zero.

         PCRE2_CONFIG_UNICODE

       The output is a uint32_t integer that is set to one if Unicode support is available; otherwise it is  set
       to zero. Unicode support implies UTF support.

         PCRE2_CONFIG_VERSION

       The  where  argument  should  point  to  a  buffer that is at least 24 code units long. (The exact length
       required can be found by calling pcre2_config() with where set to NULL.) The buffer is  filled  with  the
       PCRE2  version  string, zero-terminated. The number of code units used is returned. This is the length of
       the string plus one unit for the terminating zero.

COMPILING A PATTERN

       pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
         uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
         pcre2_compile_context *ccontext);

       void pcre2_code_free(pcre2_code *code);

       pcre2_code *pcre2_code_copy(const pcre2_code *code);

       pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);

       The pcre2_compile() function compiles a pattern into an internal form.   The  pattern  is  defined  by  a
       pointer  to  a  string  of  code units and a length in code units. If the pattern is zero-terminated, the
       length can be specified as PCRE2_ZERO_TERMINATED. A NULL pattern pointer with a length of zero is treated
       as  an  empty string (NULL with a non-zero length causes an error return). The function returns a pointer
       to a block of memory that contains the compiled pattern and related data, or NULL if an error occurred.

       If the compile context argument ccontext is NULL, memory for the compiled pattern is obtained by  calling
       malloc().  Otherwise, it is obtained from the same memory function that was used for the compile context.
       The caller must free  the  memory  by  calling  pcre2_code_free()  when  it  is  no  longer  needed.   If
       pcre2_code_free() is called with a NULL argument, it returns immediately, without doing anything.

       The  function  pcre2_code_copy()  makes  a copy of the compiled code in new memory, using the same memory
       allocator as was used for the original. However, if the code has been processed by the JIT compiler  (see
       below),  the  JIT  information  cannot  be  copied  (because it is position-dependent).  The new copy can
       initially be used only for non-JIT matching, though it can be passed to pcre2_jit_compile() if  required.
       If pcre2_code_copy() is called with a NULL argument, it returns NULL.

       The  pcre2_code_copy()  function  provides a way for individual threads in a multithreaded application to
       acquire a private copy of shared compiled code.  However, it does not make a copy of the character tables
       used  by the compiled pattern; the new pattern code points to the same tables as the original code.  (See
       "Locale Support" below for details of these character tables.) In many applications the same  tables  are
       used  throughout,  so  this  behaviour is appropriate. Nevertheless, there are occasions when a copy of a
       compiled pattern and the relevant tables are  needed.  The  pcre2_code_copy_with_tables()  provides  this
       facility.  Copies of both the code and the tables are made, with the new code pointing to the new tables.
       The memory for the new tables is automatically freed when pcre2_code_free() is called for the new copy of
       the compiled code. If pcre2_code_copy_with_tables() is called with a NULL argument, it returns NULL.

       NOTE:  When  one  of  the  matching functions is called, pointers to the compiled pattern and the subject
       string are set in the match data block so that  they  can  be  referenced  by  the  substring  extraction
       functions  after  a  successful  match.  After running a match, you must not free a compiled pattern or a
       subject string until after all operations on the match data block have taken place, unless, in  the  case
       of  the  subject  string,  you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is described in the
       section entitled "Option bits for pcre2_match()" below.

       The options argument for pcre2_compile() contains various bit settings that affect  the  compilation.  It
       should  be zero if none of them are required. The available options are described below. Some of them (in
       particular, those that are compatible with Perl, but some others as well) can also be set and unset  from
       within the pattern (see the detailed description in the pcre2pattern documentation).

       For  those  options  that can be different in different parts of the pattern, the contents of the options
       argument specifies their settings at the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and
       PCRE2_NO_UTF_CHECK options can be set at the time of matching as well as at compile time.

       Some  additional  options  and less frequently required compile-time parameters (for example, the newline
       setting) can be provided in a compile context (as described above).

       If errorcode or erroroffset is NULL, pcre2_compile() returns NULL immediately. Otherwise,  the  variables
       to  which  these  point are set to an error code and an offset (number of code units) within the pattern,
       respectively, when pcre2_compile() returns NULL because a compilation error has occurred.

       There are over 100 positive error codes that pcre2_compile() may return if  it  finds  an  error  in  the
       pattern.  There  are  also  some negative error codes that are used for invalid UTF strings when validity
       checking is in force. These are the same  as  given  by  pcre2_match()  and  pcre2_dfa_match(),  and  are
       described  in  the  pcre2unicode documentation. There is no separate documentation for the positive error
       codes, because the textual error messages that are  obtained  by  calling  the  pcre2_get_error_message()
       function (see "Obtaining a textual error message" below) should be self-explanatory. Macro names starting
       with PCRE2_ERROR_ are defined for both positive and negative error codes in pcre2.h. When compilation  is
       successful   errorcode   is   set  to  a  value  that  returns  the  message  "no  error"  if  passed  to
       pcre2_get_error_message().

       The value returned in erroroffset is an indication of where in the pattern an error occurred. When  there
       is no error, zero is returned. A non-zero value is not necessarily the furthest point in the pattern that
       was read. For example, after the error "lookbehind assertion is  not  fixed  length",  the  error  offset
       points  to  the start of the failing assertion. For an invalid UTF-8 or UTF-16 string, the offset is that
       of the first code unit of the failing character.

       Some errors are not detected until the whole pattern has been scanned; in these cases, the offset  passed
       back  is  the length of the pattern. Note that the offset is in code units, not characters, even in a UTF
       mode. It may sometimes point into the middle of a UTF-8 or UTF-16 character.

       This code fragment shows a typical straightforward call to pcre2_compile():

         pcre2_code *re;
         PCRE2_SIZE erroffset;
         int errorcode;
         re = pcre2_compile(
           "^A.*Z",                /* the pattern */
           PCRE2_ZERO_TERMINATED,  /* the pattern is zero-terminated */
           0,                      /* default options */
           &errorcode,             /* for error code */
           &erroffset,             /* for error offset */
           NULL);                  /* no compile context */

   Main compile options

       The following names for option bits are defined in the pcre2.h header file:

         PCRE2_ANCHORED

       If this bit is set, the pattern is forced to be "anchored", that is, it is constrained to match  only  at
       the  first  matching  point  in the string that is being searched (the "subject string"). This effect can
       also be achieved by appropriate constructs in the pattern itself, which is the only way to do it in Perl.

         PCRE2_ALLOW_EMPTY_CLASS

       By default, for compatibility with Perl, a closing square bracket that immediately follows an opening one
       is  treated  as  a  data  character for the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the
       class, which therefore contains no characters and so can never match.

         PCRE2_ALT_BSUX

       This option request alternative handling of three escape sequences, which makes  PCRE2's  behaviour  more
       like ECMAscript (aka JavaScript). When it is set:

       (1)  \U  matches  an upper case "U" character; by default \U causes a compile time error (Perl uses \U to
       upper case subsequent characters).

       (2) \u matches a lower case "u" character unless it is followed by four hexadecimal digits, in which case
       the  hexadecimal number defines the code point to match. By default, \u causes a compile time error (Perl
       uses it to upper case the following character).

       (3) \x matches a lower case "x" character unless it is followed by two hexadecimal digits, in which  case
       the  hexadecimal  number defines the code point to match. By default, as in Perl, a hexadecimal number is
       always expected after \x, but it may have zero, one, or two digits (so, for example, \xz matches a binary
       zero character followed by z).

       ECMAscript  6  added  additional functionality to \u. This can be accessed using the PCRE2_EXTRA_ALT_BSUX
       extra option (see "Extra compile options" below).  Note that this  alternative  escape  handling  applies
       only  to  patterns.  Neither  of  these  options  affects the processing of replacement strings passed to
       pcre2_substitute().

         PCRE2_ALT_CIRCUMFLEX

       In multiline mode (when PCRE2_MULTILINE is set), the circumflex metacharacter matches at the start of the
       subject  (unless  PCRE2_NOTBOL  is  set), and also after any internal newline. However, it does not match
       after a newline at the end of the  subject,  for  compatibility  with  Perl.  If  you  want  a  multiline
       circumflex also to match after a terminating newline, you must set PCRE2_ALT_CIRCUMFLEX.

         PCRE2_ALT_EXTENDED_CLASS

       Alters  the  parsing  of character classes to follow the extended syntax described by Unicode UTS#18. The
       PCRE2_ALT_EXTENDED_CLASS option has no impact on the behaviour of the Perl-specific "(?[...])" syntax for
       extended  classes, but instead enables the alternative syntax of extended class behaviour inside ordinary
       "[...]" character classes. See the pcre2pattern  documentation  for  details  of  the  character  classes
       supported.

         PCRE2_ALT_VERBNAMES

       By  default,  for  compatibility  with  Perl,  the  name in any verb sequence such as (*MARK:NAME) is any
       sequence of characters that does not include a closing parenthesis. The name is not processed in any way,
       and  it is not possible to include a closing parenthesis in the name. However, if the PCRE2_ALT_VERBNAMES
       option is set, normal backslash processing is applied  to  verb  names  and  only  an  unescaped  closing
       parenthesis  terminates the name. A closing parenthesis can be included in a name either as \) or between
       \Q and \E. If the PCRE2_EXTENDED or PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, unescaped
       whitespace in verb names is skipped and #-comments are recognized, exactly as in the rest of the pattern.

         PCRE2_AUTO_CALLOUT

       If this bit is set, pcre2_compile() automatically inserts callout items, all with number 255, before each
       pattern item, except immediately before or after an explicit callout in the pattern.  For  discussion  of
       the callout facility, see the pcre2callout documentation.

         PCRE2_CASELESS

       If  this bit is set, letters in the pattern match both upper and lower case letters in the subject. It is
       equivalent to Perl's /i option, and it can be changed within a pattern  by  a  (?i)  option  setting.  If
       either  PCRE2_UTF  or PCRE2_UCP is set, Unicode properties are used for all characters with more than one
       other case, and for all characters whose code points are greater than U+007F.

       Note that there are two ASCII characters,  K  and  S,  that,  in  addition  to  their  lower  case  ASCII
       equivalents,  are  case-equivalent  with U+212A (Kelvin sign) and U+017F (long S) respectively. If you do
       not want this case equivalence, you can suppress it by setting PCRE2_EXTRA_CASELESS_RESTRICT.

       One language family, Turkish and Azeri, has its own case-insensitivity rules, which can  be  selected  by
       setting PCRE2_EXTRA_TURKISH_CASING. This alters the behaviour of the 'i', 'I', U+0130 (capital I with dot
       above), and U+0131 (small dotless i) characters.

       For lower valued characters with only one other case, a lookup table is  used  for  speed.  When  neither
       PCRE2_UTF nor PCRE2_UCP is set, a lookup table is used for all code points less than 256, and higher code
       points (available only in 16-bit or 32-bit mode) are treated as not having another case.

       From release 10.45 PCRE2_CASELESS also affects what some of the letter-related Unicode  property  escapes
       (\p  and  \P)  match.  The  properties Lu (upper case letter), Ll (lower case letter), and Lt (title case
       letter) are all treated as LC (cased letter) when PCRE2_CASELESS is set.

         PCRE2_DOLLAR_ENDONLY

       If this bit is set, a dollar metacharacter in the pattern matches only at the end of the subject  string.
       Without this option, a dollar also matches immediately before a newline at the end of the string (but not
       before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored if PCRE2_MULTILINE is  set.  There
       is no equivalent to this option in Perl, and no way to set it within a pattern.

         PCRE2_DOTALL

       If  this  bit  is  set,  a  dot  metacharacter  in  the pattern matches any character, including one that
       indicates a newline. However, it only ever matches one character, even if newlines  are  coded  as  CRLF.
       Without  this option, a dot does not match when the current position in the subject is at a newline. This
       option is equivalent to Perl's /s option, and it can be  changed  within  a  pattern  by  a  (?s)  option
       setting.  A  negative  class  such  as [^a] always matches newline characters, and the \N escape sequence
       always matches a non-newline character, independent of the setting of PCRE2_DOTALL.

         PCRE2_DUPNAMES

       If this bit is set, names used to identify capture groups need not be unique.  This can  be  helpful  for
       certain  types of pattern when it is known that only one instance of the named group can ever be matched.
       There are more details of named capture groups below; see also the pcre2pattern documentation.

         PCRE2_ENDANCHORED

       If this bit is set, the end of any pattern match must be right at the end of the  string  being  searched
       (the  "subject  string"). If the pattern match succeeds by reaching (*ACCEPT), but does not reach the end
       of the subject, the match fails at the current starting point. For unanchored patterns, a  new  match  is
       then tried at the next starting point. However, if the match succeeds by reaching the end of the pattern,
       but not the end of the subject, backtracking occurs and an alternative match may be found. Consider these
       two patterns:

         .(*ACCEPT)|..
         .|..

       If  matched  against  "abc"  with PCRE2_ENDANCHORED set, the first matches "c" whereas the second matches
       "bc". The effect of PCRE2_ENDANCHORED can also be achieved  by  appropriate  constructs  in  the  pattern
       itself, which is the only way to do it in Perl.

       For  DFA  matching  with  pcre2_dfa_match(),  PCRE2_ENDANCHORED  applies  only to the first (that is, the
       longest) matched string. Other parallel matches, which are necessarily substrings of the first one,  must
       obviously end before the end of the subject.

         PCRE2_EXTENDED

       If  this  bit is set, most white space characters in the pattern are totally ignored except when escaped,
       inside a character class, or inside a \Q...\E sequence.  However,  white  space  is  not  allowed  within
       sequences  such as (?> that introduce various parenthesized groups, nor within numerical quantifiers such
       as {1,3}. Ignorable white space is permitted between an item and a following  quantifier  and  between  a
       quantifier  and  a  following  + that indicates possessiveness. PCRE2_EXTENDED is equivalent to Perl's /x
       option, and it can be changed within a pattern by a (?x) option setting.

       When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED  recognizes  as  white  space  only  those
       characters with code points less than 256 that are flagged as white space in its low-character table. The
       table is normally created by pcre2_maketables(), which uses the  isspace()  function  to  identify  space
       characters.  In most ASCII environments, the relevant characters are those with code points 0x0009 (tab),
       0x000A (linefeed), 0x000B (vertical  tab),  0x000C  (formfeed),  0x000D  (carriage  return),  and  0x0020
       (space).

       When  PCRE2 is compiled with Unicode support, in addition to these characters, five more Unicode "Pattern
       White Space" characters are recognized by PCRE2_EXTENDED. These are U+0085 (next line), U+200E  (left-to-
       right mark), U+200F (right-to-left mark), U+2028 (line separator), and U+2029 (paragraph separator). This
       set of characters is the same as recognized by Perl's /x option. Note that the  horizontal  and  vertical
       space characters that are matched by the \h and \v escapes in patterns are a much bigger set.

       As  well  as  ignoring  most  white  space,  PCRE2_EXTENDED also causes characters between an unescaped #
       outside a character class and the next newline, inclusive, to be ignored,  which  makes  it  possible  to
       include  comments  inside  complicated  patterns.  Note that the end of this type of comment is a literal
       newline sequence in the pattern; escape sequences that happen to represent a newline do not count.

       Which characters are interpreted as newlines can be specified by a setting in the compile context that is
       passed  to  pcre2_compile()  or  by  a  special sequence at the start of the pattern, as described in the
       section entitled "Newline conventions" in the pcre2pattern documentation. A default is defined when PCRE2
       is built.

         PCRE2_EXTENDED_MORE

       This  option  has  the  effect  of  PCRE2_EXTENDED,  but, in addition, unescaped space and horizontal tab
       characters are ignored inside a character class. Note: only these two characters  are  ignored,  not  the
       full   set   of   pattern   white   space   characters  that  are  ignored  outside  a  character  class.
       PCRE2_EXTENDED_MORE is equivalent to Perl's /xx option, and it can be changed within a pattern by a (?xx)
       option setting.

         PCRE2_FIRSTLINE

       If this option is set, the start of an unanchored pattern match must be before or at the first newline in
       the subject string following the start of matching,  though  the  matched  text  may  continue  over  the
       newline.  If  startoffset  is  non-zero, the limiting newline is not necessarily the first newline in the
       subject. For example, if the subject  string  is  "abc\nxyz"  (where  \n  represents  a  single-character
       newline)  a  pattern  match  for "yz" succeeds with PCRE2_FIRSTLINE if startoffset is greater than 3. See
       also PCRE2_USE_OFFSET_LIMIT, which provides a more general limiting facility. If PCRE2_FIRSTLINE  is  set
       with  an  offset  limit,  a match must occur in the first line and also within the offset limit. In other
       words, whichever limit comes first is used. This option has no effect for anchored patterns.

         PCRE2_LITERAL

       If this option is set, all meta-characters in the pattern are disabled, and it is treated  as  a  literal
       string.  Matching literal strings with a regular expression engine is not the most efficient way of doing
       it. If you are doing a lot of literal matching and are worried  about  efficiency,  you  should  consider
       using  other  approaches.  The  only  other  main  options  that  are  allowed  with  PCRE2_LITERAL  are:
       PCRE2_ANCHORED,     PCRE2_ENDANCHORED,     PCRE2_AUTO_CALLOUT,      PCRE2_CASELESS,      PCRE2_FIRSTLINE,
       PCRE2_MATCH_INVALID_UTF,       PCRE2_NO_START_OPTIMIZE,      PCRE2_NO_UTF_CHECK,      PCRE2_UTF,      and
       PCRE2_USE_OFFSET_LIMIT. The extra options  PCRE2_EXTRA_MATCH_LINE  and  PCRE2_EXTRA_MATCH_WORD  are  also
       supported. Any other options cause an error.

         PCRE2_MATCH_INVALID_UTF

       This  option  forces  PCRE2_UTF  (see  below)  and  also enables support for matching by pcre2_match() in
       subject strings that contain invalid UTF sequences.  Note, however, that  the  16-bit  and  32-bit  PCRE2
       libraries  process  strings  as sequences of uint16_t or uint32_t code points. They cannot find valid UTF
       sequences within an arbitrary string of bytes unless such sequences are suitably aligned.  This  facility
       is not supported for DFA matching. For details, see the pcre2unicode documentation.

         PCRE2_MATCH_UNSET_BACKREF

       If this option is set, a backreference to an unset capture group matches an empty string (by default this
       causes the current matching alternative to fail).  A pattern such as (\1)(a) succeeds when this option is
       set  (assuming  it  can find an "a" in the subject), whereas it fails by default, for Perl compatibility.
       Setting this option makes PCRE2 behave more like ECMAscript (aka JavaScript).

         PCRE2_MULTILINE

       By default, for the purposes of matching "start of line" and "end of  line",  PCRE2  treats  the  subject
       string as consisting of a single line of characters, even if it actually contains newlines. The "start of
       line" metacharacter (^) matches only at the start of the string, and the "end of line" metacharacter  ($)
       matches  only at the end of the string, or before a terminating newline (except when PCRE2_DOLLAR_ENDONLY
       is set). Note, however, that unless PCRE2_DOTALL is set, the "any character" metacharacter (.)  does  not
       match at a newline. This behaviour (for ^, $, and dot) is the same as Perl.

       When  PCRE2_MULTILINE  it  is  set,  the  "start  of line" and "end of line" constructs match immediately
       following or immediately before internal newlines in the subject string, respectively, as well as at  the
       very  start  and end. This is equivalent to Perl's /m option, and it can be changed within a pattern by a
       (?m) option setting. Note that the "start of line" metacharacter does not match after a  newline  at  the
       end  of  the  subject,  for  compatibility  with  Perl.   However,  you  can  change  this by setting the
       PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a subject string, or no occurrences of ^ or $ in
       a pattern, setting PCRE2_MULTILINE has no effect.

         PCRE2_NEVER_BACKSLASH_C

       This  option  locks  out  the  use  of  \C  in the pattern that is being compiled.  This escape can cause
       unpredictable behaviour in UTF-8 or UTF-16 modes, because it may leave the current matching point in  the
       middle  of  a  multi-code-unit character. This option may be useful in applications that process patterns
       from external sources. Note that there is also a build-time option that permanently locks out the use  of
       \C.

         PCRE2_NEVER_UCP

       This option locks out the use of Unicode properties for handling \B, \b, \D, \d, \S, \s, \W, \w, and some
       of the POSIX character classes, as described for the PCRE2_UCP option below. In particular,  it  prevents
       the  creator  of the pattern from enabling this facility by starting the pattern with (*UCP). This option
       may be useful in applications that  process  patterns  from  external  sources.  The  option  combination
       PCRE2_UCP and PCRE2_NEVER_UCP causes an error.

         PCRE2_NEVER_UTF

       This  option  locks  out  interpretation  of  the pattern as UTF-8, UTF-16, or UTF-32, depending on which
       library is in use. In particular,  it  prevents  the  creator  of  the  pattern  from  switching  to  UTF
       interpretation  by  starting  the  pattern  with  (*UTF).  This option may be useful in applications that
       process patterns from external sources. The combination of PCRE2_UTF and PCRE2_NEVER_UTF causes an error.

         PCRE2_NO_AUTO_CAPTURE

       If this option is set, it disables the use of numbered capturing parentheses in the pattern. Any  opening
       parenthesis  that  is  not  followed  by ? behaves as if it were followed by ?: but named parentheses can
       still be used for capturing (and they acquire numbers in the usual way). This is the same  as  Perl's  /n
       option.   Note  that,  when  this  option  is  set,  references  to  capture  groups  (backreferences  or
       recursion/subroutine calls) may only refer to named groups, though the reference can be  by  name  or  by
       number.

         PCRE2_NO_AUTO_POSSESS

       If  this  (deprecated) option is set, it disables "auto-possessification", which is an optimization that,
       for example, turns a+b into a++b in order to avoid backtracks into  a+  that  can  never  be  successful.
       However,  if callouts are in use, auto-possessification means that some callouts are never taken. You can
       set this option if you want the matching functions to do a  full  unoptimized  search  and  run  all  the
       callouts, but it is mainly provided for testing purposes.

       If  a  compile  context  is  available,  it is recommended to use pcre2_set_optimize() with the directive
       PCRE2_AUTO_POSSESS_OFF   rather   than   the   compile   option    PCRE2_NO_AUTO_POSSESS.    Note    that
       PCRE2_NO_AUTO_POSSESS   takes   precedence   over   the   pcre2_set_optimize()   optimization  directives
       PCRE2_AUTO_POSSESS and PCRE2_AUTO_POSSESS_OFF.

         PCRE2_NO_DOTSTAR_ANCHOR

       If this (deprecated) option is set, it disables an optimization that is applied  when  .*  is  the  first
       significant  item  in  a  top-level branch of a pattern, and all the other branches also start with .* or
       with \A or \G or ^. The optimization is automatically disabled for .* if it is inside an atomic group  or
       a  capture  group that is the subject of a backreference, or if the pattern contains (*PRUNE) or (*SKIP).
       When the optimization is not disabled, such a pattern is automatically anchored if  PCRE2_DOTALL  is  set
       for  all  the .* items and PCRE2_MULTILINE is not set for any ^ items. Otherwise, the fact that any match
       must start either at the start  of  the  subject  or  following  a  newline  is  remembered.  Like  other
       optimizations,  this  can  cause  callouts  to  be  skipped.   (If  a compile context is available, it is
       recommended to use pcre2_set_optimize() with the directive PCRE2_DOTSTAR_ANCHOR_OFF instead.)

         PCRE2_NO_START_OPTIMIZE

       This is an option whose main effect is  at  matching  time.  It  does  not  change  what  pcre2_compile()
       generates,  but  it  does  affect  the  output  of the JIT compiler. Setting this option is equivalent to
       calling pcre2_set_optimize() with the directive parameter set to PCRE2_START_OPTIMIZE_OFF.

       There are a number of optimizations that may occur at the start of a match, in  order  to  speed  up  the
       process. For example, if it is known that an unanchored match must start with a specific code unit value,
       the matching code searches the subject for that value, and  fails  immediately  if  it  cannot  find  it,
       without  actually running the main matching function. The start-up optimizations are in effect a pre-scan
       of the subject that takes place before the pattern is run.

       Disabling the start-up optimizations may cause performance to suffer. However, this may be desirable  for
       patterns  which  contain  callouts  or  items such as (*COMMIT) and (*MARK). See the above description of
       PCRE2_START_OPTIMIZE_OFF for further details.

         PCRE2_NO_UTF_CHECK

       When PCRE2_UTF is set, the validity of the pattern as a UTF string is automatically  checked.  There  are
       discussions  about  the validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode
       document. If an invalid UTF sequence is found, pcre2_compile() returns a negative error code.

       If you know that your pattern is a valid UTF string, and you want to  skip  this  check  for  performance
       reasons,  you can set the PCRE2_NO_UTF_CHECK option. When it is set, the effect of passing an invalid UTF
       string as a pattern is undefined. It may cause your program to crash or loop.

       Note that this option can also be passed to pcre2_match() and pcre2_dfa_match(), to suppress UTF validity
       checking of the subject string.

       Note  also that setting PCRE2_NO_UTF_CHECK at compile time does not disable the error that is given if an
       escape sequence for an invalid Unicode code point is encountered in the pattern. In particular,  the  so-
       called "surrogate" code points (0xd800 to 0xdfff) are invalid. If you want to allow escape sequences such
       as \x{d800} you can set the PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described in the section
       entitled  "Extra  compile  options"  below.   However,  this  is possible only in UTF-8 and UTF-32 modes,
       because these values are not representable in UTF-16.

         PCRE2_UCP

       This option has two effects. Firstly, it change the way PCRE2 processes \B, \b, \D, \d, \S, \s,  \W,  \w,
       and  some  of  the  POSIX  character  classes.  By  default, only ASCII characters are recognized, but if
       PCRE2_UCP is set, Unicode properties are used to classify characters. There are some PCRE2_EXTRA  options
       (see  below)  that  add finer control to this behaviour. More details are given in the section on generic
       character types in the pcre2pattern page.

       The second effect of PCRE2_UCP is  to  force  the  use  of  Unicode  properties  for  upper/lower  casing
       operations, even when PCRE2_UTF is not set. This makes it possible to process strings in the 16-bit UCS-2
       code. This option is available only if PCRE2 has  been  compiled  with  Unicode  support  (which  is  the
       default).

       The  PCRE2_EXTRA_CASELESS_RESTRICT  option  (see  above)  restricts  caseless  matching  such  that ASCII
       characters match only ASCII characters and non-ASCII characters  match  only  non-ASCII  characters.  The
       PCRE2_EXTRA_TURKISH_CASING  option  (see above) alters the matching of the 'i' characters to follow their
       behaviour in Turkish and Azeri  languages.  For  further  details  on  PCRE2_EXTRA_CASELESS_RESTRICT  and
       PCRE2_EXTRA_TURKISH_CASING, see the pcre2unicode page.

         PCRE2_UNGREEDY

       This  option  inverts  the  "greediness"  of  the quantifiers so that they are not greedy by default, but
       become greedy if followed by "?". It is not compatible with Perl. It can also be set  by  a  (?U)  option
       setting within the pattern.

         PCRE2_USE_OFFSET_LIMIT

       This option must be set for pcre2_compile() if pcre2_set_offset_limit() is going to be used to set a non-
       default offset limit in a match context for matches that use this pattern. An error is  generated  if  an
       offset   limit   is   set   without   this   option.   For   more   details,   see   the  description  of
       pcre2_set_offset_limit() in the section that describes  match  contexts.  See  also  the  PCRE2_FIRSTLINE
       option above.

         PCRE2_UTF

       This  option  causes  PCRE2  to  regard  both  the  pattern and the subject strings that are subsequently
       processed as strings of UTF characters instead of single-code-unit strings. It is available when PCRE2 is
       built  to include Unicode support (which is the default). If Unicode support is not available, the use of
       this option provokes an error. Details of how PCRE2_UTF changes the behaviour of PCRE2 are given  in  the
       pcre2unicode page. In particular, note that it changes the way PCRE2_CASELESS works.

   Extra compile options

       The  option  bits  that  can be set in a compile context by calling the pcre2_set_compile_extra_options()
       function are as follows:

         PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK

       Since release 10.38 PCRE2 has forbidden the use of \K  within  lookaround  assertions,  following  Perl's
       lead. This option is provided to re-enable the previous behaviour (act in positive lookarounds, ignore in
       negative ones) in case anybody is relying on it.

         PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES

       This option applies when compiling a pattern in UTF-8 or UTF-32 mode. It is forbidden in UTF-16 mode, and
       ignored in non-UTF modes. Unicode "surrogate" code points in the range 0xd800 to 0xdfff are used in pairs
       in UTF-16 to encode code points with values in the range  0x10000  to  0x10ffff.  The  surrogates  cannot
       therefore  be  represented  in  UTF-16.  They  can be represented in UTF-8 and UTF-32, but are defined as
       invalid code points, and cause errors if encountered in a UTF-8 or UTF-32 string that  is  being  checked
       for validity by PCRE2.

       These  values  also  cause  errors  if encountered in escape sequences such as \x{d912} within a pattern.
       However, it seems that some applications, when using PCRE2 to check  for  unwanted  characters  in  UTF-8
       strings,  explicitly  test  for the surrogates using escape sequences. The PCRE2_NO_UTF_CHECK option does
       not disable the error that occurs, because it applies only to  the  testing  of  input  strings  for  UTF
       validity.

       If  the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surrogate code point values in UTF-8 and
       UTF-32 patterns no longer provoke errors and are incorporated in the compiled pattern. However, they  can
       only match subject characters if the matching function is called with PCRE2_NO_UTF_CHECK set.

         PCRE2_EXTRA_ALT_BSUX

       The original option PCRE2_ALT_BSUX causes PCRE2 to process \U, \u, and \x in the way that ECMAscript (aka
       JavaScript) does. Additional functionality was defined by ECMAscript 6; setting PCRE2_EXTRA_ALT_BSUX  has
       the  effect  of  PCRE2_ALT_BSUX, but in addition it recognizes \u{hhh..} as a hexadecimal character code,
       where hhh.. is any number of hexadecimal digits.

         PCRE2_EXTRA_ASCII_BSD

       This option forces \d to match only ASCII digits, even when PCRE2_UCP is set.  It can be changed within a
       pattern by means of the (?aD) option setting.

         PCRE2_EXTRA_ASCII_BSS

       This option forces \s to match only ASCII space characters, even when PCRE2_UCP is set. It can be changed
       within a pattern by means of the (?aS) option setting.

         PCRE2_EXTRA_ASCII_BSW

       This option forces \w to match only ASCII word characters, even when PCRE2_UCP is set. It can be  changed
       within a pattern by means of the (?aW) option setting.

         PCRE2_EXTRA_ASCII_DIGIT

       This  option forces the POSIX character classes [:digit:] and [:xdigit:] to match only ASCII digits, even
       when PCRE2_UCP is set. It can be changed within a pattern by means of the (?aT) option setting.

         PCRE2_EXTRA_ASCII_POSIX

       This option forces all the POSIX character classes, including [:digit:] and  [:xdigit:],  to  match  only
       ASCII  characters,  even  when PCRE2_UCP is set. It can be changed within a pattern by means of the (?aP)
       option setting, but note that this also sets PCRE2_EXTRA_ASCII_DIGIT  in  order  to  ensure  that  (?-aP)
       unsets all ASCII restrictions for POSIX classes.

         PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL

       This  is  a dangerous option. Use with care. By default, an unrecognized escape such as \j or a malformed
       one such as \x{2z} causes a compile-time  error  when  detected  by  pcre2_compile().  Perl  is  somewhat
       inconsistent  in  handling  such  items: for example, \j is treated as a literal "j", and non-hexadecimal
       digits in \x{} are just ignored, though warnings are given in both cases  if  Perl's  warning  switch  is
       enabled. However, a malformed octal number after \o{ always causes an error in Perl.

       If  the  PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL extra option is passed to pcre2_compile(), all unrecognized or
       malformed escape sequences are treated as single-character escapes. For example, \j is a literal "j"  and
       \x{2z}  is treated as the literal string "x{2z}". Setting this option means that typos in patterns may go
       undetected and have unexpected results. Also note that a sequence such  as  [\N{]  is  interpreted  as  a
       malformed  attempt  at  [\N{...}]  and  so  is  treated  as  [N{]  whereas [\N] gives an error because an
       unqualified \N is a valid escape sequence but is not supported in a character class. To  reiterate:  this
       is a dangerous option. Use with great care.

         PCRE2_EXTRA_CASELESS_RESTRICT

       When  either PCRE2_UCP or PCRE2_UTF is set, caseless matching follows Unicode rules, which allow for more
       than two cases per character. There are two case-equivalent character sets that contain  both  ASCII  and
       non-ASCII  characters. The ASCII letter S is case-equivalent to U+017f (long S) and the ASCII letter K is
       case-equivalent to U+212a (Kelvin sign). This option disables recognition of case-equivalences that cross
       the ASCII/non-ASCII boundary. In a caseless match, both characters must either be ASCII or non-ASCII. The
       option can be changed within a pattern by the (*CASELESS_RESTRICT) or (?r) option settings.

         PCRE2_EXTRA_ESCAPED_CR_IS_LF

       There are some legacy applications where the escape sequence \r in a  pattern  is  expected  to  match  a
       newline.  If  this  option  is set, \r in a pattern is converted to \n so that it matches a LF (linefeed)
       instead of a CR (carriage return) character. The option does not affect a literal CR in the pattern,  nor
       does it affect CR specified as an explicit code point such as \x{0D}.

         PCRE2_EXTRA_MATCH_LINE

       This  option  is  provided  for  use  by  the -x option of pcre2grep. It causes the pattern only to match
       complete lines. This is achieved by automatically inserting the code for  "^(?:"  at  the  start  of  the
       compiled  pattern  and ")$" at the end. Thus, when PCRE2_MULTILINE is set, the matched line may be in the
       middle of the subject string. This option can be used with PCRE2_LITERAL.

         PCRE2_EXTRA_MATCH_WORD

       This option is provided for use by the -w option of pcre2grep.  It  causes  the  pattern  only  to  match
       strings  that  have a word boundary at the start and the end. This is achieved by automatically inserting
       the code for "\b(?:" at the start of the compiled pattern and ")\b" at the end. The option  may  be  used
       with PCRE2_LITERAL. However, it is ignored if PCRE2_EXTRA_MATCH_LINE is also set.

         PCRE2_EXTRA_NO_BS0

       If this option is set (note that its final character is the digit 0) it locks out the use of the sequence
       \0 unless at least one more octal digit follows.

         PCRE2_EXTRA_PYTHON_OCTAL

       If this option is set, PCRE2 follows Python's rules for interpreting octal escape  sequences.  The  rules
       for  handling  sequences  such  as \14, which could be an octal number or a back reference are different.
       Details are given in the pcre2pattern documentation.

         PCRE2_EXTRA_NEVER_CALLOUT

       If  this  option  is  set,  PCRE2  treats  callouts  in  the  pattern  as  a  syntax   error,   returning
       PCRE2_ERROR_CALLOUT_CALLER_DISABLED.  This  is useful if the application knows that a callout will not be
       provided to pcre2_match(), so that callouts in the pattern are not silently ignored.

         PCRE2_EXTRA_TURKISH_CASING

       This option alters case-equivalence of the 'i' letters to follow the alphabet used by Turkish  and  Azeri
       languages.  The option can be changed within a pattern by the (*TURKISH_CASING) start-of-pattern setting.
       Either the UTF or UCP options must be set. In the 8-bit library, UTF must be set. This option  cannot  be
       combined with PCRE2_EXTRA_CASELESS_RESTRICT.

JUST-IN-TIME (JIT) COMPILATION

       int pcre2_jit_compile(pcre2_code *code, uint32_t options);

       int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);

       pcre2_jit_stack *pcre2_jit_stack_create(size_t startsize,
         size_t maxsize, pcre2_general_context *gcontext);

       void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
         pcre2_jit_callback callback_function, void *callback_data);

       void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);

       These  functions  provide  support for JIT compilation, which, if the just-in-time compiler is available,
       further processes a compiled pattern into machine code that executes much faster than  the  pcre2_match()
       interpretive matching function. Full details are given in the pcre2jit documentation.

       JIT compilation is a heavyweight optimization. It can take some time for patterns to be analyzed, and for
       one-off matches and simple patterns the benefit of faster execution might be  offset  by  a  much  slower
       compilation time.  Most (but not all) patterns can be optimized by the JIT compiler.

LOCALE SUPPORT

       const uint8_t *pcre2_maketables(pcre2_general_context *gcontext);

       void pcre2_maketables_free(pcre2_general_context *gcontext,
         const uint8_t *tables);

       PCRE2  handles  caseless matching, and determines whether characters are letters, digits, or whatever, by
       reference to a set of tables, indexed by character code point. However, this applies only  to  characters
       whose code points are less than 256. By default, higher-valued code points never match escapes such as \w
       or \d.

       When PCRE2 is built with Unicode support (the default),  certain  Unicode  character  properties  can  be
       tested  with  \p  and  \P, or, alternatively, the PCRE2_UCP option can be set when a pattern is compiled;
       this causes \w and friends to use Unicode property support instead of  the  built-in  tables.   PCRE2_UCP
       also  causes upper/lower casing operations on characters with code points greater than 127 to use Unicode
       properties. These effects apply even when PCRE2_UTF is not set.  There  are,  however,  some  PCRE2_EXTRA
       options (see above) that can be used to modify or suppress them.

       The  use  of locales with Unicode is discouraged. If you are handling characters with code points greater
       than 127, you should either use Unicode support, or use locales, but not try to mix the two.

       PCRE2 contains a built-in set of character tables that are used by default.   These  are  sufficient  for
       many  applications. Normally, the internal tables recognize only ASCII characters. However, when PCRE2 is
       built, it is possible to cause the internal tables to be rebuilt in the default "C" locale of  the  local
       system, which may cause them to be different.

       The  built-in  tables can be overridden by tables supplied by the application that calls PCRE2. These may
       be created in a different locale from the default.   As  more  and  more  applications  change  to  using
       Unicode, the need for this locale support is expected to die away.

       External  tables  are  built by calling the pcre2_maketables() function, in the relevant locale. The only
       argument to this function is a general context, which can be used to pass a custom memory  allocator.  If
       the  argument  is NULL, the system malloc() is used. The result can be passed to pcre2_compile() as often
       as necessary, by creating a compile context and calling pcre2_set_character_tables() to  set  the  tables
       pointer therein.

       For  example,  to  build  and  use  tables  that  are  appropriate  for the French locale (where accented
       characters with values greater than 127 are treated as letters), the following code could be used:

         setlocale(LC_CTYPE, "fr_FR");
         tables = pcre2_maketables(NULL);
         ccontext = pcre2_compile_context_create(NULL);
         pcre2_set_character_tables(ccontext, tables);
         re = pcre2_compile(..., ccontext);

       The locale name "fr_FR" is used on Linux and other Unix-like systems; if you are using Windows, the  name
       for the French locale is "french".

       The  pointer  that  is  passed  (via  the  compile context) to pcre2_compile() is saved with the compiled
       pattern, and the same tables  are  used  by  the  matching  functions.  Thus,  for  any  single  pattern,
       compilation  and  matching  both  happen  in  the same locale, but different patterns can be processed in
       different locales.

       It is the caller's responsibility to ensure that the memory containing the tables remains available while
       they   are   still   in   use.   When   they   are   no   longer  needed,  you  can  discard  them  using
       pcre2_maketables_free(), which should pass as its first parameter the same global context that  was  used
       to create the tables.

   Saving locale tables

       The  tables described above are just a sequence of binary bytes, which makes them independent of hardware
       characteristics such as endianness or whether the processor is 32-bit or 64-bit. A copy of the result  of
       pcre2_maketables()  can  therefore be saved in a file or elsewhere and re-used later, even in a different
       program or on another computer. The size of the tables (number of bytes)  must  be  obtained  by  calling
       pcre2_config() with the PCRE2_CONFIG_TABLES_LENGTH option because pcre2_maketables() does not return this
       value. Note that the pcre2_dftables program, which is part of the PCRE2 build system, can be used  stand-
       alone  to  create  a  file  that  contains  a  set of binary tables. See the pcre2build documentation for
       details.

INFORMATION ABOUT A COMPILED PATTERN

       int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);

       The pcre2_pattern_info() function returns general information about a compiled pattern.  For  information
       about  callouts,  see  the next section.  The first argument for pcre2_pattern_info() is a pointer to the
       compiled pattern. The second argument specifies which piece of information is  required,  and  the  third
       argument  is  a  pointer  to  a  variable  to  receive the data. If the third argument is NULL, the first
       argument is ignored, and the function returns the size in bytes of the variable that is required for  the
       information  requested. Otherwise, the yield of the function is zero for success, or one of the following
       negative numbers:

         PCRE2_ERROR_NULL           the argument code was NULL
         PCRE2_ERROR_BADMAGIC       the "magic number" was not found
         PCRE2_ERROR_BADOPTION      the value of what was invalid
         PCRE2_ERROR_UNSET          the requested field is not set

       The "magic number" is placed at the start of each compiled pattern as a simple check against  passing  an
       arbitrary  memory  pointer.  Here  is a typical call of pcre2_pattern_info(), to obtain the length of the
       compiled pattern:

         int rc;
         size_t length;
         rc = pcre2_pattern_info(
           re,               /* result of pcre2_compile() */
           PCRE2_INFO_SIZE,  /* what is required */
           &length);         /* where to put the data */

       The possible values for the second argument are defined in pcre2.h, and are as follows:

         PCRE2_INFO_ALLOPTIONS
         PCRE2_INFO_ARGOPTIONS
         PCRE2_INFO_EXTRAOPTIONS

       Return copies of the pattern's  options.  The  third  argument  should  point  to  a  uint32_t  variable.
       PCRE2_INFO_ARGOPTIONS   returns  exactly  the  options  that  were  passed  to  pcre2_compile(),  whereas
       PCRE2_INFO_ALLOPTIONS returns the compile options as modified by any  top-level  (*XXX)  option  settings
       such as (*UTF) at the start of the pattern itself. PCRE2_INFO_EXTRAOPTIONS returns the extra options that
       were set in the compile context by calling the pcre2_set_compile_extra_options() function.

       For example, if the pattern /(*UTF)abc/ is compiled  with  the  PCRE2_EXTENDED  option,  the  result  for
       PCRE2_INFO_ALLOPTIONS  is  PCRE2_EXTENDED  and  PCRE2_UTF.   Option settings such as (?i) that can change
       within a pattern do not affect the result of PCRE2_INFO_ALLOPTIONS, even if  they  appear  right  at  the
       start of the pattern. (This was different in some earlier releases.)

       A  pattern  compiled  without  PCRE2_ANCHORED is automatically anchored by PCRE2 if the first significant
       item in every top-level branch is one of the following:

         ^     unless PCRE2_MULTILINE is set
         \A    always
         \G    always
         .*    sometimes - see below

       When .* is the first significant item, anchoring is possible only when all the following are true:

         .* is not in an atomic group
         .* is not in a capture group that is the subject
              of a backreference
         PCRE2_DOTALL is in force for .*
         Neither (*PRUNE) nor (*SKIP) appears in the pattern
         PCRE2_NO_DOTSTAR_ANCHOR is not set
         Dotstar anchoring has not been disabled with PCRE2_DOTSTAR_ANCHOR_OFF

       For patterns that are  auto-anchored,  the  PCRE2_ANCHORED  bit  is  set  in  the  options  returned  for
       PCRE2_INFO_ALLOPTIONS.

         PCRE2_INFO_BACKREFMAX

       Return  the  number  of  the  highest  backreference in the pattern. The third argument should point to a
       uint32_t variable. Named capture groups acquire numbers as well as names, and  these  count  towards  the
       highest  backreference.  Backreferences  such  as \4 or \g{12} match the captured characters of the given
       group, but in addition, the check that a capture group is set in a conditional group such as (?(3)a|b) is
       also a backreference.  Zero is returned if there are no backreferences.

         PCRE2_INFO_BSR

       The  output  is  a uint32_t integer whose value indicates what character sequences the \R escape sequence
       matches. A value of PCRE2_BSR_UNICODE means that \R matches any Unicode line ending sequence; a value  of
       PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF.

         PCRE2_INFO_CAPTURECOUNT

       Return  the  highest capture group number in the pattern. In patterns where (?| is not used, this is also
       the total number of capture groups. The third argument should point to a uint32_t variable.

         PCRE2_INFO_DEPTHLIMIT

       If the pattern set a backtracking depth limit by including an item of the form (*LIMIT_DEPTH=nnnn) at the
       start, the value is returned. The third argument should point to a uint32_t integer. If no such value has
       been set, the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. Note that this limit will
       only  be  used  during  matching if it is less than the limit set or defaulted by the caller of the match
       function.

         PCRE2_INFO_FIRSTBITMAP

       In the absence of a single first code unit for a non-anchored pattern, pcre2_compile()  may  construct  a
       256-bit  table  that  defines  a fixed set of values for the first code unit in any match. For example, a
       pattern that starts with [abc] results in a table with three bits set. When code unit values greater than
       255  are supported, the flag bit for 255 means "any code unit of value 255 or above". If such a table was
       constructed, a pointer to it is returned. Otherwise NULL is returned. The third argument should point  to
       a const uint8_t * variable.

         PCRE2_INFO_FIRSTCODETYPE

       Return information about the first code unit of any matched string, for a non-anchored pattern. The third
       argument should point to a uint32_t variable. If there is a fixed first value, for  example,  the  letter
       "c"  from  a  pattern  such  as  (cat|cow|coyote),  1  is  returned, and the value can be retrieved using
       PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed first value, but it is known that a match can  occur  only
       at  the  start  of  the  subject or following a newline in the subject, 2 is returned. Otherwise, and for
       anchored patterns, 0 is returned.

         PCRE2_INFO_FIRSTCODEUNIT

       Return  the  value  of  the  first  code   unit   of   any   matched   string   for   a   pattern   where
       PCRE2_INFO_FIRSTCODETYPE  returns  1;  otherwise  return 0. The third argument should point to a uint32_t
       variable. In the 8-bit library, the value is always less than 256. In the 16-bit library the value can be
       up  to 0xffff. In the 32-bit library in UTF-32 mode the value can be up to 0x10ffff, and up to 0xffffffff
       when not using UTF-32 mode.

         PCRE2_INFO_FRAMESIZE

       Return the size (in bytes) of the data frames that are used to remember backtracking positions  when  the
       pattern is processed by pcre2_match() without the use of JIT. The third argument should point to a size_t
       variable. The frame size depends on the number of capturing parentheses in the pattern.  Each  additional
       capture group adds two PCRE2_SIZE variables.

         PCRE2_INFO_HASBACKSLASHC

       Return  1  if the pattern contains any instances of \C, otherwise 0. The third argument should point to a
       uint32_t variable.

         PCRE2_INFO_HASCRORLF

       Return 1 if the pattern contains any explicit matches for CR or LF characters,  otherwise  0.  The  third
       argument  should  point to a uint32_t variable. An explicit match is either a literal CR or LF character,
       or \r or \n or one of the equivalent hexadecimal or octal escape sequences.

         PCRE2_INFO_HEAPLIMIT

       If the pattern set a heap memory limit by including an item of the form (*LIMIT_HEAP=nnnn) at the  start,
       the  value  is returned. The third argument should point to a uint32_t integer. If no such value has been
       set, the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. Note that this limit will only
       be  used  during  matching  if  it  is  less  than  the limit set or defaulted by the caller of the match
       function.

         PCRE2_INFO_JCHANGED

       Return 1 if the (?J) or (?-J) option setting is used in the pattern,  otherwise  0.  The  third  argument
       should  point  to  a  uint32_t  variable.  (?J)  and (?-J) set and unset the local PCRE2_DUPNAMES option,
       respectively.

         PCRE2_INFO_JITSIZE

       If the compiled pattern was successfully processed by pcre2_jit_compile(), return the  size  of  the  JIT
       compiled code, otherwise return zero. The third argument should point to a size_t variable.

         PCRE2_INFO_LASTCODETYPE

       Returns  1 if there is a rightmost literal code unit that must exist in any matched string, other than at
       its start. The third argument should point to a uint32_t variable. If  there  is  no  such  value,  0  is
       returned.  When 1 is returned, the code unit value itself can be retrieved using PCRE2_INFO_LASTCODEUNIT.
       For anchored patterns, a last literal value is recorded only if it follows something of variable  length.
       For   example,   for   the  pattern  /^a\d+z\d+/  the  returned  value  is  1  (with  "z"  returned  from
       PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is 0.

         PCRE2_INFO_LASTCODEUNIT

       Return the value of the rightmost literal code unit that must exist in any matched string, other than  at
       its start, for a pattern where PCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return 0. The third argument
       should point to a uint32_t variable.

         PCRE2_INFO_MATCHEMPTY

       Return 1 if the pattern might match an empty string, otherwise 0. The third argument should  point  to  a
       uint32_t  variable.  When  a  pattern  contains  recursive  subroutine calls it is not always possible to
       determine whether or not it can match an empty string. PCRE2 takes a cautious approach and returns  1  in
       such cases.

         PCRE2_INFO_MATCHLIMIT

       If  the  pattern set a match limit by including an item of the form (*LIMIT_MATCH=nnnn) at the start, the
       value is returned. The third argument should point to a uint32_t integer. If no such value has been  set,
       the  call  to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET. Note that this limit will only be
       used during matching if it is less than the limit set or defaulted by the caller of the match function.

         PCRE2_INFO_MAXLOOKBEHIND

       A lookbehind assertion moves back a certain number of characters (not  code  units)  when  it  starts  to
       process  each  of  its  branches.  This  request  returns  the largest of these backward moves. The third
       argument should point to a uint32_t integer. The simple assertions \b  and  \B  require  a  one-character
       lookbehind  and  cause  PCRE2_INFO_MAXLOOKBEHIND  to  return 1 in the absence of anything longer. \A also
       registers a one-character lookbehind, though it does not actually inspect the previous character.

       Note that this information is useful for multi-segment matching only if the pattern  contains  no  nested
       lookbehinds.  For  example,  the pattern (?<=a(?<=ba)c) returns a maximum lookbehind of 2, but when it is
       processed, the first lookbehind moves back by two characters, matches  one  character,  then  the  nested
       lookbehind  also moves back by two characters. This puts the matching point three characters earlier than
       it was at the start.  PCRE2_INFO_MAXLOOKBEHIND is really  only  useful  as  a  debugging  tool.  See  the
       pcre2partial documentation for a discussion of multi-segment matching.

         PCRE2_INFO_MINLENGTH

       If  a  minimum  length  for  matching  subject strings was computed, its value is returned. Otherwise the
       returned value is 0. This value is not computed when PCRE2_NO_START_OPTIMIZE  is  set.  The  value  is  a
       number  of  characters,  which  in  UTF  mode  may  be different from the number of code units. The third
       argument should point to a uint32_t variable. The value is a lower bound to the length  of  any  matching
       string.  There  may  not be any strings of that length that do actually match, but every string that does
       match is at least that long.

         PCRE2_INFO_NAMECOUNT
         PCRE2_INFO_NAMEENTRYSIZE
         PCRE2_INFO_NAMETABLE

       PCRE2 supports the use of named as well  as  numbered  capturing  parentheses.  The  names  are  just  an
       additional way of identifying the parentheses, which still acquire numbers. Several convenience functions
       such as pcre2_substring_get_byname() are provided for extracting captured substrings by name. It is  also
       possible  to  extract  the data directly, by first converting the name to a number in order to access the
       correct pointers in the output vector (described with pcre2_match() below). To  do  the  conversion,  you
       need to use the name-to-number map, which is described by these three values.

       The map consists of a number of fixed-size entries. PCRE2_INFO_NAMECOUNT gives the number of entries, and
       PCRE2_INFO_NAMEENTRYSIZE gives the size of each entry in code units; both  of  these  return  a  uint32_t
       value. The entry size depends on the length of the longest name.

       PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table. This is a PCRE2_SPTR pointer to a
       block of code units. In the 8-bit library, the first two bytes of  each  entry  are  the  number  of  the
       capturing  parenthesis,  most significant byte first. In the 16-bit library, the pointer points to 16-bit
       code units, the first of which contains the parenthesis number. In the 32-bit library, the pointer points
       to  32-bit  code  units, the first of which contains the parenthesis number. The rest of the entry is the
       corresponding name, zero terminated.

       The names are in alphabetical order. If (?| is used to create  multiple  capture  groups  with  the  same
       number,  as  described in the section on duplicate group numbers in the pcre2pattern page, the groups may
       be given the same name, but there is only one entry in the table. Different names for groups of the  same
       number are not permitted.

       Duplicate  names  for  capture groups with different numbers are permitted, but only if PCRE2_DUPNAMES is
       set. They appear in the table in the order in which they were found in the pattern. In the absence of (?|
       this  is  the order of increasing number; when (?| is used this is not necessarily the case because later
       capture groups may have lower numbers.

       As a simple example of the name/number table, consider the following pattern  after  compilation  by  the
       8-bit library (assume PCRE2_EXTENDED is set, so white space - including newlines - is ignored):

         (?<date> (?<year>(\d\d)?\d\d) -
         (?<month>\d\d) - (?<day>\d\d) )

       There  are four named capture groups, so the table has four entries, and each entry in the table is eight
       bytes long. The table is as follows, with non-printing bytes shows in hexadecimal,  and  undefined  bytes
       shown as ??:

         00 01 d  a  t  e  00 ??
         00 05 d  a  y  00 ?? ??
         00 04 m  o  n  t  h  00
         00 02 y  e  a  r  00 ??

       When  writing  code to extract data from named capture groups using the name-to-number map, remember that
       the length of the entries is likely to be different for each compiled pattern.

         PCRE2_INFO_NEWLINE

       The output is one of the following uint32_t values:

         PCRE2_NEWLINE_CR       Carriage return (CR)
         PCRE2_NEWLINE_LF       Linefeed (LF)
         PCRE2_NEWLINE_CRLF     Carriage return, linefeed (CRLF)
         PCRE2_NEWLINE_ANY      Any Unicode line ending
         PCRE2_NEWLINE_ANYCRLF  Any of CR, LF, or CRLF
         PCRE2_NEWLINE_NUL      The NUL character (binary zero)

       This identifies the character sequence that will be recognized as meaning "newline" while matching.

         PCRE2_INFO_SIZE

       Return the size of the compiled pattern in bytes (for all three libraries).  The  third  argument  should
       point to a size_t variable. This value includes the size of the general data block that precedes the code
       units of the compiled pattern itself. The value that is used when pcre2_compile() is  getting  memory  in
       which  to  place  the  compiled  pattern  may  be slightly larger than the value returned by this option,
       because there are cases where the code that calculates  the  size  has  to  over-estimate.  Processing  a
       pattern with the JIT compiler does not alter the value returned by this option.

INFORMATION ABOUT A PATTERN'S CALLOUTS

       int pcre2_callout_enumerate(const pcre2_code *code,
         int (*callback)(pcre2_callout_enumerate_block *, void *),
         void *user_data);

       A  script  language  that  supports  the  use  of string arguments in callouts might like to scan all the
       callouts in a pattern before running the match. This can be done  by  calling  pcre2_callout_enumerate().
       The  first argument is a pointer to a compiled pattern, the second points to a callback function, and the
       third is arbitrary user data. The callback function is called for every callout in  the  pattern  in  the
       order  in  which  they  appear.  Its  first argument is a pointer to a callout enumeration block, and its
       second argument is the user_data value that was passed to pcre2_callout_enumerate(). The contents of  the
       callout  enumeration  block  are  described  in  the pcre2callout documentation, which also gives further
       details about callouts.

SERIALIZATION AND PRECOMPILING

       It is possible to save compiled patterns on disc or elsewhere, and reload them later, subject to a number
       of  restrictions.  The host on which the patterns are reloaded must be running the same version of PCRE2,
       with the same code unit width, and must also have the same  endianness,  pointer  width,  and  PCRE2_SIZE
       type.  Before compiled patterns can be saved, they must be converted to a "serialized" form, which in the
       case of PCRE2 is really just a bytecode dump.  The functions whose names begin with pcre2_serialize_  are
       used  for  converting  to  and  from  the  serialized  form.  They  are  described  in the pcre2serialize
       documentation. Note that PCRE2 serialization does not convert compiled patterns  to  an  abstract  format
       like Java or .NET serialization.

THE MATCH DATA BLOCK

       pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
         pcre2_general_context *gcontext);

       pcre2_match_data *pcre2_match_data_create_from_pattern(
         const pcre2_code *code, pcre2_general_context *gcontext);

       void pcre2_match_data_free(pcre2_match_data *match_data);

       Information  about a successful or unsuccessful match is placed in a match data block, which is an opaque
       structure that is accessed by function calls. In particular, the match data block contains  a  vector  of
       offsets  into  the  subject  string  that  define  the matched parts of the subject. This is known as the
       ovector.

       Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match() you must create a match data  block
       by  calling one of the creation functions above. For pcre2_match_data_create(), the first argument is the
       number of pairs of offsets in the ovector.

       When using pcre2_match(), one pair of offsets is required to identify the string that matched  the  whole
       pattern,  with  an  additional pair for each captured substring. For example, a value of 4 creates enough
       space to record the matched portion of the subject plus three captured substrings.

       When using pcre2_dfa_match() there may be multiple matched substrings of different lengths  at  the  same
       point in the subject. The ovector should be made large enough to hold as many as are expected.

       A  minimum of at least 1 pair is imposed by pcre2_match_data_create(), so it is always possible to return
       the overall matched  string  in  the  case  of  pcre2_match()  or  the  longest  match  in  the  case  of
       pcre2_dfa_match().   The   maximum   number   of   pairs   is   65535;   if   the   first   argument   of
       pcre2_match_data_create() is greater than this, 65535 is used.

       The second argument of pcre2_match_data_create() is a pointer to a general  context,  which  can  specify
       custom  memory  management for obtaining the memory for the match data block. If you are not using custom
       memory management, pass NULL, which causes malloc() to be used.

       For pcre2_match_data_create_from_pattern(), the first argument is a pointer to a  compiled  pattern.  The
       ovector  is  created to be exactly the right size to hold all the substrings a pattern might capture when
       matched using pcre2_match(). You should not use this  call  when  matching  with  pcre2_dfa_match().  The
       second  argument  is again a pointer to a general context, but in this case if NULL is passed, the memory
       is obtained using the same allocator that was used for the compiled pattern (custom or default).

       A match data block can be used many times, with the same or different compiled patterns. You can  extract
       information  from  a  match  data  block  after  a match operation has finished, using functions that are
       described in the sections on matched strings and other match data below.

       When a call of pcre2_match() fails, valid data is available in the match block only  when  the  error  is
       PCRE2_ERROR_NOMATCH,  PCRE2_ERROR_PARTIAL,  or  one of the error codes for an invalid UTF string. Exactly
       what is available depends on the error, and is detailed below.

       When one of the matching functions is called, pointers to the compiled pattern and the subject string are
       set in the match data block so that they can be referenced by the extraction functions after a successful
       match. After running a match, you must not free a compiled pattern or a subject string  until  after  all
       operations  on the match data block (for that match) have taken place, unless, in the case of the subject
       string, you have used the PCRE2_COPY_MATCHED_SUBJECT option, which is described in the  section  entitled
       "Option bits for pcre2_match()" below.

       When   a   match   data   block   itself   is   no   longer   needed,  it  should  be  freed  by  calling
       pcre2_match_data_free(). If this function is called with a NULL argument, it returns immediately, without
       doing anything.

MEMORY USE FOR MATCH DATA BLOCKS

       PCRE2_SIZE pcre2_get_match_data_size(pcre2_match_data *match_data);

       PCRE2_SIZE pcre2_get_match_data_heapframes_size(
         pcre2_match_data *match_data);

       The  size  of  a  match  data  block  depends  on  the size of the ovector that it contains. The function
       pcre2_get_match_data_size() returns the size, in bytes, of the block that is its argument.

       When pcre2_match() runs interpretively (that is, without using JIT), it makes use of  a  vector  of  data
       frames  for  remembering backtracking positions.  The size of each individual frame depends on the number
       of capturing parentheses in the pattern and can be obtained  by  calling  pcre2_pattern_info()  with  the
       PCRE2_INFO_FRAMESIZE option (see the section entitled "Information about a compiled pattern" above).

       Heap  memory  is used for the frames vector; if the initial memory block turns out to be too small during
       matching, it is automatically expanded. When pcre2_match() returns, the memory is not freed, but  remains
       attached  to  the  match  data  block,  for  use by any subsequent matches that use the same block. It is
       automatically freed when the match data block itself is freed.

       You can find  the  current  size  of  the  frames  vector  that  a  match  data  block  owns  by  calling
       pcre2_get_match_data_heapframes_size().  For a newly created match data block the size will be zero. Some
       types of match may require a lot of frames and thus a large vector; applications that run in environments
       where  memory  is  constrained can check this and free the match data block if the heap frames vector has
       become too big.

MATCHING A PATTERN: THE TRADITIONAL FUNCTION

       int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext);

       The function pcre2_match() is called to match a subject string  against  a  compiled  pattern,  which  is
       passed  in the code argument. You can call pcre2_match() with the same code argument as many times as you
       like, in order to find multiple matches in the subject string or to match different subject strings  with
       the same pattern.

       This  function  is  the main matching facility of the library, and it operates in a Perl-like manner. For
       specialist use there is also an alternative matching function, which is described below  in  the  section
       about the pcre2_dfa_match() function.

       Here is an example of a simple call to pcre2_match():

         pcre2_match_data *md = pcre2_match_data_create(4, NULL);
         int rc = pcre2_match(
           re,             /* result of pcre2_compile() */
           "some string",  /* the subject string */
           11,             /* the length of the subject string */
           0,              /* start at offset 0 in the subject */
           0,              /* default options */
           md,             /* the match data block */
           NULL);          /* a match context; NULL means use defaults */

       If  the  subject  string  is  zero-terminated,  the length can be given as PCRE2_ZERO_TERMINATED. A match
       context must be provided if certain less common matching parameters are to be changed. For  details,  see
       the section on the match context above.

   The string to be matched by pcre2_match()

       The subject string is passed to pcre2_match() as a pointer in subject, a length in length, and a starting
       offset in startoffset. The length and offset are in code units, not characters.  That  is,  they  are  in
       bytes  for  the  8-bit  library,  16-bit code units for the 16-bit library, and 32-bit code units for the
       32-bit library, whether or not UTF processing is enabled. As a special  case,  if  subject  is  NULL  and
       length  is  zero, the subject is assumed to be an empty string. If length is non-zero, an error occurs if
       subject is NULL.

       If startoffset is greater than the length of the subject,  pcre2_match()  returns  PCRE2_ERROR_BADOFFSET.
       When the starting offset is zero, the search for a match starts at the beginning of the subject, and this
       is by far the most common case. In UTF-8 or UTF-16 mode, the starting offset must point to the start of a
       character,  or  to  the  end  of  the subject (in UTF-32 mode, one code unit equals one character, so all
       offsets are valid). Like the pattern string, the subject may contain binary zeros.

       A non-zero starting offset is useful when searching for another match in  the  same  subject  by  calling
       pcre2_match()  again after a previous success.  Setting startoffset differs from passing over a shortened
       string and setting PCRE2_NOTBOL in the case of a pattern that begins with any  kind  of  lookbehind.  For
       example, consider the pattern

         \Biss\B

       which  finds occurrences of "iss" in the middle of words. (\B matches only if the current position in the
       subject is not a word boundary.) When applied to the string "Mississippi" the first call to pcre2_match()
       finds  the  first  occurrence.  If  pcre2_match() is called again with just the remainder of the subject,
       namely "issippi", it does not match, because \B is always false at the start of  the  subject,  which  is
       deemed  to  be  a  word  boundary.  However, if pcre2_match() is passed the entire string again, but with
       startoffset set to 4, it finds the second occurrence of "iss" because it  is  able  to  look  behind  the
       starting point to discover that it is preceded by a letter.

       Finding all the matches in a subject is tricky when the pattern can match an empty string. It is possible
       to emulate Perl's  /g  behaviour  by  first  trying  the  match  again  at  the  same  offset,  with  the
       PCRE2_NOTEMPTY_ATSTART  and PCRE2_ANCHORED options, and then if that fails, advancing the starting offset
       and trying an ordinary match again. There is some code that demonstrates how to do this in the  pcre2demo
       sample  program.  In the most general case, you have to check to see if the newline convention recognizes
       CRLF as a newline, and if so, and the current character is CR followed by LF, advance the starting offset
       by two characters instead of one.

       If  a  non-zero  starting offset is passed when the pattern is anchored, a single attempt to match at the
       given offset is made. This can only succeed if the pattern does not require the match to be at the  start
       of  the subject. In other words, the anchoring must be the result of setting the PCRE2_ANCHORED option or
       the use of .* with PCRE2_DOTALL, not by starting the pattern with ^ or \A.

   Option bits for pcre2_match()

       The unused bits of the options argument for pcre2_match() must be zero. The only bits that may be set are
       PCRE2_ANCHORED,     PCRE2_COPY_MATCHED_SUBJECT,    PCRE2_DISABLE_RECURSELOOP_CHECK,    PCRE2_ENDANCHORED,
       PCRE2_NOTBOL, PCRE2_NOTEOL,  PCRE2_NOTEMPTY,  PCRE2_NOTEMPTY_ATSTART,  PCRE2_NO_JIT,  PCRE2_NO_UTF_CHECK,
       PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT.  Their action is described below.

       Setting  PCRE2_ANCHORED  or  PCRE2_ENDANCHORED  at  match time is not supported by the just-in-time (JIT)
       compiler. If it is set, JIT matching is disabled and the  interpretive  code  in  pcre2_match()  is  run.
       PCRE2_DISABLE_RECURSELOOP_CHECK is ignored by JIT, but apart from PCRE2_NO_JIT (obviously), the remaining
       options are supported for JIT matching.

         PCRE2_ANCHORED

       The PCRE2_ANCHORED option limits pcre2_match() to matching at the first matching position. If  a  pattern
       was  compiled  with  PCRE2_ANCHORED, or turned out to be anchored by virtue of its contents, it cannot be
       made unachored at matching time. Note that setting the option at match time disables JIT matching.

         PCRE2_COPY_MATCHED_SUBJECT

       By default, a pointer to the subject is remembered in the match data block so that,  after  a  successful
       match,  it  can be referenced by the substring extraction functions. This means that the subject's memory
       must not be freed until all such operations are complete. For some applications where the lifetime of the
       subject  string  is  not  guaranteed, it may be necessary to make a copy of the subject string, but it is
       wasteful  to   do   this   unless   the   match   is   successful.   After   a   successful   match,   if
       PCRE2_COPY_MATCHED_SUBJECT  is  set, the subject is copied and the new pointer is remembered in the match
       data block instead of the original subject pointer. The memory allocator that  was  used  for  the  match
       block  itself is used. The copy is automatically freed when pcre2_match_data_free() is called to free the
       match data block. It is also automatically freed if the match data block is  re-used  for  another  match
       operation.

         PCRE2_DISABLE_RECURSELOOP_CHECK

       This option is relevant only to pcre2_match() for interpretive matching.  It is ignored when JIT is used,
       and is forbidden for pcre2_dfa_match().

       The use of recursion in patterns can lead to infinite loops. In the interpretive matcher these  would  be
       eventually caught by the match or heap limits, but this could take a long time and/or use a lot of memory
       if the limits are large. There is therefore a check at the start of each recursion.  If the same group is
       still  active from a previous call, and the current subject pointer is the same as it was at the start of
       that group, and the furthest inspected character of the subject has not changed, an error is generated.

       There are rare cases of matches that would complete, but nevertheless trigger  this  error.  This  option
       disables the check. It is provided mainly for testing when comparing JIT and interpretive behaviour.

         PCRE2_ENDANCHORED

       If the PCRE2_ENDANCHORED option is set, any string that pcre2_match() matches must be right at the end of
       the subject string. Note that setting the option at match time disables JIT matching.

         PCRE2_NOTBOL

       This option specifies that first character of the subject string is not the beginning of a line,  so  the
       circumflex  metacharacter  should not match before it. Setting this without having set PCRE2_MULTILINE at
       compile time causes circumflex never to match. This option affects only the behaviour of  the  circumflex
       metacharacter. It does not affect \A.

         PCRE2_NOTEOL

       This  option  specifies  that  the  end  of  the  subject  string is not the end of a line, so the dollar
       metacharacter should not match it nor (except in multiline mode) a newline immediately before it. Setting
       this without having set PCRE2_MULTILINE at compile time causes dollar never to match. This option affects
       only the behaviour of the dollar metacharacter. It does not affect \Z or \z.

         PCRE2_NOTEMPTY

       An empty string is not considered to be a valid match if this option is set. If there are alternatives in
       the  pattern, they are tried. If all the alternatives match the empty string, the entire match fails. For
       example, if the pattern

         a?b?

       is applied to a string not beginning with "a" or "b", it matches an empty string  at  the  start  of  the
       subject.  With  PCRE2_NOTEMPTY  set,  this match is not valid, so pcre2_match() searches further into the
       string for occurrences of "a" or "b".

         PCRE2_NOTEMPTY_ATSTART

       This is like PCRE2_NOTEMPTY, except that it locks out an empty string match only at  the  first  matching
       position,  that  is, at the start of the subject plus the starting offset. An empty string match later in
       the subject is permitted.  If the pattern is anchored, such  a  match  can  occur  only  if  the  pattern
       contains \K.

         PCRE2_NO_JIT

       By  default,  if  a  pattern has been successfully processed by pcre2_jit_compile(), JIT is automatically
       used when pcre2_match() is called with options that JIT supports. Setting PCRE2_NO_JIT disables  the  use
       of JIT; it forces matching to be done by the interpreter.

         PCRE2_NO_UTF_CHECK

       When  PCRE2_UTF  is  set  at  compile time, the validity of the subject as a UTF string is checked unless
       PCRE2_NO_UTF_CHECK is passed to pcre2_match() or PCRE2_MATCH_INVALID_UTF was passed  to  pcre2_compile().
       The latter special case is discussed in detail in the pcre2unicode documentation.

       In  the  default  case, if a non-zero starting offset is given, the check is applied only to that part of
       the subject that could be inspected during matching, and there is a check that the starting offset points
       to the first code unit of a character or to the end of the subject. If there are no lookbehind assertions
       in the pattern, the check starts at the starting offset.  Otherwise, it  starts  at  the  length  of  the
       longest  lookbehind before the starting offset, or at the start of the subject if there are not that many
       characters before the starting offset. Note that the sequences \b and \B are one-character lookbehinds.

       The check is carried out before any other processing takes place, and a negative error code  is  returned
       if  the  check  fails.  There  are  several  UTF  error  codes for each code unit width, corresponding to
       different problems with the code unit sequence.  There  are  discussions  about  the  validity  of  UTF-8
       strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode documentation.

       If  you know that your subject is valid, and you want to skip this check for performance reasons, you can
       set the PCRE2_NO_UTF_CHECK option when calling pcre2_match(). You might want to do this  for  the  second
       and  subsequent  calls  to pcre2_match() if you are making repeated calls to find multiple matches in the
       same subject string.

       Warning: Unless PCRE2_MATCH_INVALID_UTF was set at compile time, when PCRE2_NO_UTF_CHECK is set at  match
       time  the  effect  of  passing  an  invalid  string  as a subject, or an invalid value of startoffset, is
       undefined.  Your program may crash or loop indefinitely or give wrong results.

         PCRE2_PARTIAL_HARD
         PCRE2_PARTIAL_SOFT

       These options turn on the partial matching feature. A partial match occurs if  the  end  of  the  subject
       string  is  reached  successfully,  but there are not enough subject characters to complete the match. In
       addition, either at least one  character  must  have  been  inspected  or  the  pattern  must  contain  a
       lookbehind, or the pattern must be one that could match an empty string.

       If  this situation arises when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD) is set, matching continues
       by testing any remaining alternatives. Only if no complete match  can  be  found  is  PCRE2_ERROR_PARTIAL
       returned  instead of PCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT specifies that the caller is
       prepared to handle a partial match, but only if no complete match can be found.

       If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this case, if a partial match is found,
       pcre2_match()  immediately  returns  PCRE2_ERROR_PARTIAL,  without considering any other alternatives. In
       other words, when PCRE2_PARTIAL_HARD is set, a partial match is considered to be more important  that  an
       alternative complete match.

       There  is  a  more  detailed  discussion  of  partial  and  multi-segment matching, with examples, in the
       pcre2partial documentation.

NEWLINE HANDLING WHEN MATCHING

       When PCRE2 is built, a default newline convention is set; this is usually the standard convention for the
       operating  system.  The default can be overridden in a compile context by calling pcre2_set_newline(). It
       can also be overridden by starting a pattern string with, for  example,  (*CRLF),  as  described  in  the
       section  on newline conventions in the pcre2pattern page. During matching, the newline choice affects the
       behaviour of the dot, circumflex, and dollar metacharacters. It may also alter the way the match starting
       position is advanced after a match failure for an unanchored pattern.

       When  PCRE2_NEWLINE_CRLF,  PCRE2_NEWLINE_ANYCRLF,  or PCRE2_NEWLINE_ANY is set as the newline convention,
       and a match attempt for an unanchored pattern fails when the current  starting  position  is  at  a  CRLF
       sequence,  and  the  pattern  contains no explicit matches for CR or LF characters, the match position is
       advanced by two characters instead of one, in other words, to after the CRLF.

       The above rule is a compromise that makes the most common cases work as expected.  For  example,  if  the
       pattern  is  .+A  (and the PCRE2_DOTALL option is not set), it does not match the string "\r\nA" because,
       after failing at the start, it skips both the CR and the LF before retrying. However, the pattern [\r\n]A
       does  match  that string, because it contains an explicit CR or LF reference, and so advances only by one
       character after the first failure.

       An explicit match for CR of LF is either a literal appearance of one of those characters in the  pattern,
       or one of the \r or \n or equivalent octal or hexadecimal escape sequences. Implicit matches such as [^X]
       do not count, nor does \s, even though it includes CR and LF in the characters that it matches.

       Notwithstanding the above, anomalous effects may still occur when CRLF is a valid  newline  sequence  and
       explicit \r or \n escapes appear in the pattern.

HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS

       uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);

       PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);

       In  general, a pattern matches a certain portion of the subject, and in addition, further substrings from
       the subject may be picked out by parenthesized parts of the  pattern.  Following  the  usage  in  Jeffrey
       Friedl's  book,  this  is  called  "capturing"  in  what  follows,  and  the phrase "capture group" (Perl
       terminology) is used for a fragment of a pattern that picks out a substring. PCRE2 supports several other
       kinds  of  parenthesized  group  that  do  not  cause substrings to be captured. The pcre2_pattern_info()
       function can be used to find out how many capture groups there are in a compiled pattern.

       You can use auxiliary functions for accessing captured substrings by number or by name, as  described  in
       sections below.

       Alternatively,  you  can  make  direct  use of the vector of PCRE2_SIZE values, called the ovector, which
       contains the  offsets  of  captured  strings.  It  is  part  of  the  match  data  block.   The  function
       pcre2_get_ovector_pointer() returns the address of the ovector, and pcre2_get_ovector_count() returns the
       number of pairs of values it contains.

       Within the ovector, the first in each pair of values is set to the offset of the first  code  unit  of  a
       substring, and the second is set to the offset of the first code unit after the end of a substring. These
       values are always code unit offsets, not character offsets. That is, they are byte offsets in  the  8-bit
       library, 16-bit offsets in the 16-bit library, and 32-bit offsets in the 32-bit library.

       After  a  partial  match  (error  return  PCRE2_ERROR_PARTIAL),  only the first pair of offsets (that is,
       ovector[0] and ovector[1]) are set. They identify the part of the subject that was partially matched. See
       the pcre2partial documentation for details of partial matching.

       After  a  fully  successful match, the first pair of offsets identifies the portion of the subject string
       that was matched by the entire pattern. The next pair is used for the first captured  substring,  and  so
       on. The value returned by pcre2_match() is one more than the highest numbered pair that has been set. For
       example, if two substrings have been captured, the  returned  value  is  3.  If  there  are  no  captured
       substrings, the return value from a successful match is 1, indicating that just the first pair of offsets
       has been set.

       If a pattern uses the \K escape sequence within a positive assertion, the reported start of a  successful
       match  can be greater than the end of the match.  For example, if the pattern (?=ab\K) is matched against
       "ab", the start and end offset values for the match are 2 and 0.

       If a capture group is matched repeatedly within a single match operation, it is the last portion  of  the
       subject that it matched that is returned.

       If the ovector is too small to hold all the captured substring offsets, as much as possible is filled in,
       and the function returns a value of zero. If captured substrings are not of interest,  pcre2_match()  may
       be called with a match data block whose ovector is of minimum length (that is, one pair).

       It  is  possible for capture group number n+1 to match some part of the subject when group n has not been
       used at all. For example, if the string "abc" is matched against the pattern (a|(z))(bc) the return  from
       the  function  is  4, and groups 1 and 3 are matched, but 2 is not. When this happens, both values in the
       offset pairs corresponding to unused groups are set to PCRE2_UNSET.

       Offset values that correspond to unused groups at the end of the expression are also set to  PCRE2_UNSET.
       For  example,  if  the  string "abc" is matched against the pattern (abc)(x(yz)?)? groups 2 and 3 are not
       matched. The return from the function is 2, because the highest used  capture  group  number  is  1.  The
       offsets  for the second and third capture groups (assuming the vector is large enough, of course) are set
       to PCRE2_UNSET.

       Elements in the ovector that do not correspond to capturing parentheses in the pattern are never changed.
       That  is, if a pattern contains n capturing parentheses, no more than ovector[0] to ovector[2n+1] are set
       by pcre2_match(). The other elements retain whatever values they previously had.  After  a  failed  match
       attempt, the contents of the ovector are unchanged.

OTHER INFORMATION ABOUT A MATCH

       PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);

       PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);

       As  well  as  the  offsets  in the ovector, other information about a match is retained in the match data
       block and can be retrieved by the above functions in appropriate circumstances. If  they  are  called  at
       other times, the result is undefined.

       After   a   successful   match,   a   partial   match   (PCRE2_ERROR_PARTIAL),  or  a  failure  to  match
       (PCRE2_ERROR_NOMATCH), a mark name may be available. The  function  pcre2_get_mark()  can  be  called  to
       access  this  name,  which  can be specified in the pattern by any of the backtracking control verbs, not
       just (*MARK). The same function applies to all the verbs. It returns a  pointer  to  the  zero-terminated
       name,  which is within the compiled pattern. If no name is available, NULL is returned. The length of the
       name (excluding the terminating zero) is stored in the code unit that precedes the name. You  should  use
       this length instead of relying on the terminating zero if the name might contain a binary zero.

       After  a  successful  match,  the name that is returned is the last mark name encountered on the matching
       path through the pattern. Instances of backtracking verbs without names do not count. Thus, for  example,
       if  the  matching  path  contains  (*MARK:A)(*PRUNE),  the  name "A" is returned. After a "no match" or a
       partial match, the last encountered name is returned. For example, consider this pattern:

         ^(*MARK:A)((*MARK:B)a|b)c

       When it matches "bc", the returned name is A. The B mark is "seen" in the first branch of the group,  but
       it  is  not  on the matching path. On the other hand, when this pattern fails to match "bx", the returned
       name is B.

       Warning: By default, certain start-of-match optimizations are used to give a fast "no  match"  result  in
       some  situations.  For  example,  if the anchoring is removed from the pattern above, there is an initial
       check for the presence of "c" in the subject before running the matching engine.  This  check  fails  for
       "bx",  causing a match failure without seeing any marks. You can disable the start-of-match optimizations
       by setting the PCRE2_NO_START_OPTIMIZE option  for  pcre2_compile()  or  by  starting  the  pattern  with
       (*NO_START_OPT).

       After   a  successful  match,  a  partial  match,  or  one  of  the  invalid  UTF  errors  (for  example,
       PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can be called. After  a  successful  or  partial  match  it
       returns  the  code unit offset of the character at which the match started. For a non-partial match, this
       can be different to the value of ovector[0] if the pattern contains  the  \K  escape  sequence.  After  a
       partial match, however, this value is always the same as ovector[0] because \K does not affect the result
       of a partial match.

       After a UTF check failure, pcre2_get_startchar() can be used to  obtain  the  code  unit  offset  of  the
       invalid UTF character. Details are given in the pcre2unicode page.

ERROR RETURNS FROM pcre2_match()

       If  pcre2_match()  fails, it returns a negative number. This can be converted to a text string by calling
       the pcre2_get_error_message() function (see "Obtaining a textual error message" below).   Negative  error
       codes  are  also  returned by other functions, and are documented with them. The codes are given names in
       the header file. If UTF checking is in force and an invalid UTF subject string  is  detected,  one  of  a
       number  of UTF-specific negative error codes is returned. Details are given in the pcre2unicode page. The
       following are the other errors that may be returned by pcre2_match():

         PCRE2_ERROR_NOMATCH

       The subject string did not match the pattern.

         PCRE2_ERROR_PARTIAL

       The subject string did not match, but it did match partially.  See  the  pcre2partial  documentation  for
       details of partial matching.

         PCRE2_ERROR_BADMAGIC

       PCRE2  stores  a  4-byte  "magic  number" at the start of the compiled code, to catch the case when it is
       passed a junk pointer. This is the error that is returned when the magic number is not present.

         PCRE2_ERROR_BADMODE

       This error is given when a compiled pattern is passed to a function in a library of a different code unit
       width,  for  example,  a  pattern  compiled  by the 8-bit library is passed to a 16-bit or 32-bit library
       function.

         PCRE2_ERROR_BADOFFSET

       The value of startoffset was greater than the length of the subject.

         PCRE2_ERROR_BADOPTION

       An unrecognized bit was set in the options argument.

         PCRE2_ERROR_BADUTFOFFSET

       The UTF code unit sequence that was passed  as  a  subject  was  checked  and  found  to  be  valid  (the
       PCRE2_NO_UTF_CHECK  option was not set), but the value of startoffset did not point to the beginning of a
       UTF character or the end of the subject.

         PCRE2_ERROR_CALLOUT

       This error is never generated by pcre2_match() itself. It is provided for use by callout  functions  that
       want  to  cause  pcre2_match()  or  pcre2_callout_enumerate() to return a distinctive error code. See the
       pcre2callout documentation for details.

         PCRE2_ERROR_DEPTHLIMIT

       The nested backtracking depth limit was reached.

         PCRE2_ERROR_HEAPLIMIT

       The heap limit was reached.

         PCRE2_ERROR_INTERNAL

       An unexpected internal error has occurred. This error could be caused by a bug in PCRE2 or by overwriting
       of the compiled pattern.

         PCRE2_ERROR_JIT_STACKLIMIT

       This  error  is returned when a pattern that was successfully studied using JIT is being matched, but the
       memory  available  for  the  just-in-time  processing  stack  is  not  large  enough.  See  the  pcre2jit
       documentation for more details.

         PCRE2_ERROR_MATCHLIMIT

       The backtracking match limit was reached.

         PCRE2_ERROR_NOMEMORY

       Heap  memory  is  used  to  remember  backtracking points. This error is given when the memory allocation
       function (default or custom) fails. Note that a different error, PCRE2_ERROR_HEAPLIMIT, is given  if  the
       amount   of   memory   needed   exceeds   the  heap  limit.  PCRE2_ERROR_NOMEMORY  is  also  returned  if
       PCRE2_COPY_MATCHED_SUBJECT is set and memory allocation fails.

         PCRE2_ERROR_NULL

       Either the code, subject, or match_data argument was passed as NULL.

         PCRE2_ERROR_RECURSELOOP

       This error is returned when pcre2_match() detects a recursion loop within the pattern.  Specifically,  it
       means that either the whole pattern or a capture group has been called recursively for the second time at
       the same position in the subject string. Some simple patterns that might do this are detected and faulted
       at  compile  time,  but  more  complicated  cases,  in particular mutual recursions between two different
       groups, cannot be detected until matching is attempted.

OBTAINING A TEXTUAL ERROR MESSAGE

       int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
         PCRE2_SIZE bufflen);

       A text message for an error code from any PCRE2 function (compile, match, or auxiliary) can  be  obtained
       by  calling  pcre2_get_error_message().  The code is passed as the first argument, with the remaining two
       arguments specifying a code unit buffer and its length in code units, into  which  the  text  message  is
       placed.  The  message  is  returned  in code units of the appropriate width for the library that is being
       used.

       The returned message is terminated with a trailing zero, and the function  returns  the  number  of  code
       units  used,  excluding  the  trailing  zero.  If  the  error  number is unknown, the negative error code
       PCRE2_ERROR_BADDATA is returned. If the buffer is too small, the message is truncated (but still  with  a
       trailing  zero),  and the negative error code PCRE2_ERROR_NOMEMORY is returned.  None of the messages are
       very long; a buffer size of 120 code units is ample.

EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

       int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_SIZE *length);

       int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_UCHAR *buffer,
         PCRE2_SIZE *bufflen);

       int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
         uint32_t number, PCRE2_UCHAR **bufferptr,
         PCRE2_SIZE *bufflen);

       void pcre2_substring_free(PCRE2_UCHAR *buffer);

       Captured substrings can be accessed directly by using the ovector as described above.   For  convenience,
       auxiliary  functions  are  provided  for extracting captured substrings as new, separate, zero-terminated
       strings. A substring that contains a binary zero is correctly extracted and has a further zero  added  on
       the end, but the result is not, of course, a C string.

       The functions in this section identify substrings by number. The number zero refers to the entire matched
       substring, with higher numbers referring to substrings captured by parenthesized groups. After a  partial
       match,  only  substring  zero  is  available.  An  attempt to extract any other substring gives the error
       PCRE2_ERROR_PARTIAL. The next section describes similar functions for extracting captured  substrings  by
       name.

       If  a pattern uses the \K escape sequence within a positive assertion, the reported start of a successful
       match can be greater than the end of the match.  For example, if the pattern (?=ab\K) is matched  against
       "ab",  the  start  and  end  offset  values  for  the match are 2 and 0. In this situation, calling these
       functions with a zero substring number extracts a zero-length empty string.

       You can find the length in  code  units  of  a  captured  substring  without  extracting  it  by  calling
       pcre2_substring_length_bynumber(). The first argument is a pointer to the match data block, the second is
       the group number, and the third is a pointer to a variable into which the length is placed. If  you  just
       want to know whether or not the substring has been captured, you can pass the third argument as NULL.

       The  pcre2_substring_copy_bynumber() function copies a captured substring into a supplied buffer, whereas
       pcre2_substring_get_bynumber() copies it into new memory,  obtained  using  the  same  memory  allocation
       function that was used for the match data block. The first two arguments of these functions are a pointer
       to the match data block and a capture group number.

       The final arguments of pcre2_substring_copy_bynumber() are a pointer to the buffer and  a  pointer  to  a
       variable  that  contains  its length in code units.  This is updated to contain the actual number of code
       units used for the extracted substring, excluding the terminating zero.

       For pcre2_substring_get_bynumber() the third and fourth arguments point to  variables  that  are  updated
       with  a  pointer  to  the  new  memory  and  the  number of code units that comprise the substring, again
       excluding the terminating zero. When the substring is no longer needed, the memory  should  be  freed  by
       calling pcre2_substring_free().

       The  return  value from all these functions is zero for success, or a negative error code. If the pattern
       match failed, the match failure code is returned.  If a substring number greater than zero is used  after
       a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible error codes are:

         PCRE2_ERROR_NOMEMORY

       The  buffer  was  too  small for pcre2_substring_copy_bynumber(), or the attempt to get memory failed for
       pcre2_substring_get_bynumber().

         PCRE2_ERROR_NOSUBSTRING

       There is no substring with that number in the pattern, that is, the number is greater than the number  of
       capturing parentheses.

         PCRE2_ERROR_UNAVAILABLE

       The  substring number, though not greater than the number of captures in the pattern, is greater than the
       number of slots in the ovector, so the substring could not be captured.

         PCRE2_ERROR_UNSET

       The substring did not participate in the match. For example,  if  the  pattern  is  (abc)|(def)  and  the
       subject is "def", and the ovector contains at least two capturing slots, substring number 1 is unset.

EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS

       int pcre2_substring_list_get(pcre2_match_data *match_data,
         PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);

       void pcre2_substring_list_free(PCRE2_UCHAR **list);

       The  pcre2_substring_list_get()  function extracts all available substrings and builds a list of pointers
       to them. It also (optionally) builds a second list that contains their lengths (in code units), excluding
       a  terminating  zero  that is added to each of them. All this is done in a single block of memory that is
       obtained using the same memory allocation function that was used to get the match data block.

       This function must be called only after a successful match. If called after a partial  match,  the  error
       code PCRE2_ERROR_PARTIAL is returned.

       The  address  of  the memory block is returned via listptr, which is also the start of the list of string
       pointers. The end of the list is marked by a NULL pointer. The address of the list of lengths is returned
       via  lengthsptr.  If  your strings do not contain binary zeros and you do not therefore need the lengths,
       you may supply NULL as the lengthsptr argument to disable the creation of a list of lengths. The yield of
       the function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the memory block could not be obtained.
       When the list is no longer needed, it should be freed by calling pcre2_substring_list_free().

       If this function encounters a substring that is unset, which can happen when  capture  group  number  n+1
       matches  some part of the subject, but group n has not been used at all, it returns an empty string. This
       can be distinguished from a genuine zero-length substring by inspecting the  appropriate  offset  in  the
       ovector, which contain PCRE2_UNSET for unset substrings, or by calling pcre2_substring_length_bynumber().

EXTRACTING CAPTURED SUBSTRINGS BY NAME

       int pcre2_substring_number_from_name(const pcre2_code *code,
         PCRE2_SPTR name);

       int pcre2_substring_length_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_SIZE *length);

       int pcre2_substring_copy_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);

       int pcre2_substring_get_byname(pcre2_match_data *match_data,
         PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);

       void pcre2_substring_free(PCRE2_UCHAR *buffer);

       To extract a substring by name, you first have to find associated number.  For example, for this pattern:

         (a+)b(?<xxx>\d+)...

       the  number of the capture group called "xxx" is 2. If the name is known to be unique (PCRE2_DUPNAMES was
       not set), you can find the number from the name by calling pcre2_substring_number_from_name(). The  first
       argument  is  the  compiled  pattern,  and the second is the name. The yield of the function is the group
       number, PCRE2_ERROR_NOSUBSTRING if there is no group with that name, or PCRE2_ERROR_NOUNIQUESUBSTRING  if
       there  is  more  than one group with that name.  Given the number, you can extract the substring directly
       from the ovector, or use one of the "bynumber" functions described above.

       For convenience, there are also "byname" functions that correspond to the "bynumber" functions, the  only
       difference  being  that  the  second argument is a name instead of a number. If PCRE2_DUPNAMES is set and
       there are duplicate names, these functions scan all the groups  with  the  given  name,  and  return  the
       captured substring from the first named group that is set.

       If  there  are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is returned. If all groups with the
       name have numbers that are greater than the number of slots in the  ovector,  PCRE2_ERROR_UNAVAILABLE  is
       returned.  If  there  is  at least one group with a slot in the ovector, but no group is found to be set,
       PCRE2_ERROR_UNSET is returned.

       Warning: If the pattern uses the (?| feature to set up multiple capture groups with the same  number,  as
       described  in  the  section  on duplicate group numbers in the pcre2pattern page, you cannot use names to
       distinguish the different capture groups, because names are  not  included  in  the  compiled  code.  The
       matching  process uses only numbers. For this reason, the use of different names for groups with the same
       number causes an error at compile time.

CREATING A NEW STRING WITH SUBSTITUTIONS

       int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext, PCRE2_SPTR replacement,
         PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
         PCRE2_SIZE *outlengthptr);

       This function optionally calls pcre2_match() and then makes a copy of the subject string in outputbuffer,
       replacing parts that were matched with the replacement string, whose length is supplied in rlength, which
       can be given as PCRE2_ZERO_TERMINATED for a zero-terminated string. As a special case, if replacement  is
       NULL  and  rlength  is zero, the replacement is assumed to be an empty string. If rlength is non-zero, an
       error occurs if replacement is NULL.

       There is  an  option  (see  PCRE2_SUBSTITUTE_REPLACEMENT_ONLY  below)  to  return  just  the  replacement
       string(s).  The default action is to perform just one replacement if the pattern matches, but there is an
       option that requests multiple replacements (see PCRE2_SUBSTITUTE_GLOBAL below).

       If successful, pcre2_substitute() returns the number of substitutions that were carried out. This may  be
       zero  if  no  match  was  found,  and  is never greater than one unless PCRE2_SUBSTITUTE_GLOBAL is set. A
       negative value is returned if an error is detected.

       Matches in which a \K item in a lookahead in the pattern causes the match to end before it starts are not
       supported, and give rise to an error return. For global replacements, matches in which \K in a lookbehind
       causes the match to start earlier than the point that was reached in the previous iteration are also  not
       supported.

       The  first  seven  arguments  of  pcre2_substitute()  are  the same as for pcre2_match(), except that the
       partial matching options are not permitted, and match_data may be passed as NULL, in which case  a  match
       data  block  is obtained and freed within this function, using memory management functions from the match
       context, if provided, or else those that were used to allocate memory for the compiled code.

       If match_data is not NULL and PCRE2_SUBSTITUTE_MATCHED is not set, the provided block  is  used  for  all
       calls to pcre2_match(), and its contents afterwards are the result of the final call. For global changes,
       this will always be a no-match error. The contents of the ovector within the match data block may or  may
       not have been changed.

       As  well as the usual options for pcre2_match(), a number of additional options can be set in the options
       argument of pcre2_substitute().  One such option  is  PCRE2_SUBSTITUTE_MATCHED.  When  this  is  set,  an
       external  match_data  block  must be provided, and it must have already been used for an external call to
       pcre2_match() with the same pattern and subject arguments. The data in the match_data block (return code,
       offset  vector)  is  then  used  for  the first substitution instead of calling pcre2_match() from within
       pcre2_substitute(). This allows an application to check  for  a  match  before  choosing  to  substitute,
       without having to repeat the match.

       The contents of the externally supplied match data block are not changed when PCRE2_SUBSTITUTE_MATCHED is
       set. If PCRE2_SUBSTITUTE_GLOBAL is also set, pcre2_match() is called  after  the  first  substitution  to
       check  for  further  matches, but this is done using an internally obtained match data block, thus always
       leaving the external block unchanged.

       The code argument is not used for matching before the first substitution when PCRE2_SUBSTITUTE_MATCHED is
       set,  but  it  must  be  provided,  even  when  PCRE2_SUBSTITUTE_GLOBAL  is  not set, because it contains
       information such as the UTF setting and the number of capturing parentheses in the pattern.

       The default action of pcre2_substitute() is  to  return  a  copy  of  the  subject  string  with  matched
       substrings   replaced.  However,  if  PCRE2_SUBSTITUTE_REPLACEMENT_ONLY  is  set,  only  the  replacement
       substrings are returned. In the global case, multiple replacements are concatenated in the output buffer.
       Substitution callouts (see below) can be used to separate them if necessary.

       The  outlengthptr  argument  of  pcre2_substitute() must point to a variable that contains the length, in
       code units, of the output buffer. If the function is successful, the value  is  updated  to  contain  the
       length in code units of the new string, excluding the trailing zero that is automatically added.

       If  the  function  is  not  successful,  the value set via outlengthptr depends on the type of error. For
       syntax errors in the replacement string, the value is the offset in  the  replacement  string  where  the
       error  was detected. For other errors, the value is PCRE2_UNSET by default. This includes the case of the
       output buffer being too small, unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set.

       PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output buffer is too  small.  The  default
       action  is to return PCRE2_ERROR_NOMEMORY immediately. If this option is set, however, pcre2_substitute()
       continues to go through the motions of matching and substituting (without, of course,  writing  anything)
       in  order  to  compute  the  size  of  buffer  that is needed, which will include the extra space for the
       terminating NUL. This value is passed back via the outlengthptr variable, with the result of the function
       still being PCRE2_ERROR_NOMEMORY.

       Passing  a  buffer  size  of  zero  is a permitted way of finding out how much memory is needed for given
       substitution. However, this does mean that the entire operation is carried out twice.  Depending  on  the
       application,  it may be more efficient to allocate a large buffer and free the excess afterwards, instead
       of using PCRE2_SUBSTITUTE_OVERFLOW_LENGTH.

       The replacement string, which is interpreted as a UTF string in UTF mode, is  checked  for  UTF  validity
       unless  PCRE2_NO_UTF_CHECK  is set. An invalid UTF replacement string causes an immediate return with the
       relevant UTF error code.

       If PCRE2_SUBSTITUTE_LITERAL is set, the replacement string is not interpreted in  any  way.  By  default,
       however,  a  dollar  character  is  an escape character that can specify the insertion of characters from
       capture groups and names from (*MARK) or other control verbs in the pattern. Dollar is  the  only  escape
       character (backslash is treated as literal). The following forms are recognized:

         $$                  insert a dollar character
         $n or ${n}          insert the contents of group n
         $0 or $&            insert the entire matched substring
         $`                  insert the substring that precedes the match
         $'                  insert the substring that follows the match
         $_                  insert the entire input string
         $*MARK or ${*MARK}  insert a control verb name

       Either  a  group  number  or a group name can be given for n, for example $2 or $NAME. Curly brackets are
       required only if the following character would be interpreted as part of the number or name.  The  number
       may  be  zero  to  include  the  entire matched string. For example, if the pattern a(b)c is matched with
       "=abc=" and the replacement string "+$1$0$1+", the result is "=+babcb+=".

       The JavaScript form $<name>, where the angle brackets are part of the  syntax,  is  also  recognized  for
       group names, but not for group numbers or *MARK.

       $*MARK inserts the name from the last encountered backtracking control verb on the matching path that has
       a name. (*MARK) must always include a name, but the other verbs need not. For example,  in  the  case  of
       (*MARK:A)(*PRUNE)  the  name  inserted is "A", but for (*MARK:A)(*PRUNE:B) the relevant name is "B". This
       facility can be used to perform simple simultaneous substitutions, as this pcre2test example shows:

         /(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*MARK}
             apple lemon
          2: pear orange

       PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject string, replacing every  matching
       substring.  If  this  option  is  not  set, only the first matching substring is replaced. The search for
       matches takes place in the original subject string (that is, previous replacements  do  not  affect  it).
       Iteration  is  implemented by advancing the startoffset value for each search, which is always passed the
       entire subject string. If an offset limit is set in the match context, searching stops when that limit is
       reached.

       You can restrict the effect of a global substitution to a portion of the subject string by setting either
       or both of startoffset and an offset limit. Here is a pcre2test example:

         /B/g,replace=!,use_offset_limit
         ABC ABC ABC ABC\=offset=3,offset_limit=12
          2: ABC A!C A!C ABC

       When continuing with global substitutions after matching a substring with zero length, an attempt to find
       a  non-empty match at the same offset is performed.  If this is not successful, the offset is advanced by
       one character except when CRLF is a valid newline sequence and the next two characters  are  CR,  LF.  In
       this case, the offset is advanced by two characters.

       PCRE2_SUBSTITUTE_UNKNOWN_UNSET  causes  references to capture groups that do not appear in the pattern to
       be treated as unset groups. This option should be used with care, because it means that a typo in a group
       name or number no longer causes the PCRE2_ERROR_NOSUBSTRING error.

       PCRE2_SUBSTITUTE_UNSET_EMPTY    causes    unset   capture   groups   (including   unknown   groups   when
       PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be treated as empty strings when inserted as  described  above.
       If  this  option is not set, an attempt to insert an unset group causes the PCRE2_ERROR_UNSET error. This
       option does not influence the extended substitution syntax described below.

       PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to the replacement string.  Without  this
       option,  only the dollar character is special, and only the group insertion forms listed above are valid.
       When PCRE2_SUBSTITUTE_EXTENDED is set, several things change:

       Firstly, backslash in a replacement string is interpreted as an escape character. The usual forms such as
       \x{ddd} can be used to specify particular character codes, and backslash followed by any non-alphanumeric
       character quotes that character. Extended quoting can be coded  using  \Q...\E,  exactly  as  in  pattern
       strings.  The  escapes  \b  and  \v  are  interpreted  as  the  characters  backspace  and  vertical tab,
       respectively.

       The interpretation of backslash followed by one or more digits is the same as in a pattern, which in Perl
       has some ambiguities. Details are given in the pcre2pattern page.

       The  Python  form  \g<n>, where the angle brackets are part of the syntax and n is either a group name or
       number, is recognized as an altertive way of inserting the contents of a group, for example \g<3>.

       There are also four escape sequences for forcing the case of inserted letters.  Case forcing  applies  to
       all inserted characters, including those from capture groups and letters within \Q...\E quoted sequences.
       The insertion mechanism has three states: no case forcing, force upper case, and force  lower  case.  The
       escape sequences change the current state: \U and \L change to upper or lower case forcing, respectively,
       and \E (when not terminating a \Q quoted sequence) reverts to no case forcing. The sequences  \u  and  \l
       force  the  next  character  (if it is a letter) to upper or lower case, respectively, and then the state
       automatically reverts to no case forcing.

       However, if \u is immediately followed by \L or \l is immediately followed by \U,  the  next  character's
       case  is  forced  by  the first escape sequence, and subsequent characters by the second. This provides a
       "title casing" facility that can be applied to group captures. For  example,  if  group  1  has  captured
       "heLLo", the replacement string "\u\L$1" becomes "Hello".

       If  either  PCRE2_UTF or PCRE2_UCP was set when the pattern was compiled, Unicode properties are used for
       case forcing characters whose code points are greater than 127. However, only  simple  case  folding,  as
       determined  by  the  Unicode  file CaseFolding.txt is supported. PCRE2 does not support language-specific
       special casing rules such as using different lower case Greek sigmas in the middle and ends of words  (as
       defined in the Unicode file SpecialCasing.txt).

       Note  that  case  forcing  sequences  such  as \U...\E do not nest. For example, the result of processing
       "\Uaa\LBB\Ecc\E" is "AAbbcc"; the final  \E  has  no  effect.  Note  also  that  the  PCRE2_ALT_BSUX  and
       PCRE2_EXTRA_ALT_BSUX options do not apply to replacement strings.

       The  final  effect  of  setting  PCRE2_SUBSTITUTE_EXTENDED  is  to  add more flexibility to capture group
       substitution. The syntax is similar to that used by Bash:

         ${n:-string}
         ${n:+string1:string2}

       As in the simple case, n may be a group number or a name. The first form specifies a  default  value.  If
       group n is set, its value is inserted; if not, the string is expanded and the result inserted. The second
       form specifies strings that are expanded and inserted when group n is set  or  unset,  respectively.  The
       first form is just a convenient shorthand for

         ${n:+${n}:string}

       Backslash can be used to escape colons and closing curly brackets in the replacement strings. A change of
       the case forcing state within a replacement  string  remains  in  force  afterwards,  as  shown  in  this
       pcre2test example:

         /(some)?(body)/substitute_extended,replace=${1:+\U:\L}HeLLo
             body
          1: hello
             somebody
          1: HELLO

       The   PCRE2_SUBSTITUTE_UNSET_EMPTY   option  does  not  affect  these  extended  substitutions.  However,
       PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause unknown groups in the extended syntax forms to  be  treated  as
       unset.

       If  PCRE2_SUBSTITUTE_LITERAL  is  set,  PCRE2_SUBSTITUTE_UNKNOWN_UNSET, PCRE2_SUBSTITUTE_UNSET_EMPTY, and
       PCRE2_SUBSTITUTE_EXTENDED are irrelevant and are ignored.

   Substitution errors

       In  the  event  of  an  error,  pcre2_substitute()  returns   a   negative   error   code.   Except   for
       PCRE2_ERROR_NOMATCH (which is never returned), errors from pcre2_match() are passed straight back.

       PCRE2_ERROR_NOSUBSTRING    is    returned    for    a    non-existent    substring    insertion,   unless
       PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set.

       PCRE2_ERROR_UNSET is returned for an unset substring  insertion  (including  an  unknown  substring  when
       PCRE2_SUBSTITUTE_UNKNOWN_UNSET   is   set)   when   the   simple   (non-extended)   syntax  is  used  and
       PCRE2_SUBSTITUTE_UNSET_EMPTY is not set.

       PCRE2_ERROR_NOMEMORY   is   returned   if   the   output   buffer   is   not   big   enough.    If    the
       PCRE2_SUBSTITUTE_OVERFLOW_LENGTH  option  is  set,  the  size  of  buffer  that is needed is returned via
       outlengthptr. Note that this does not happen by default.

       PCRE2_ERROR_NULL is returned if PCRE2_SUBSTITUTE_MATCHED is set but the match_data argument is NULL or if
       the  subject  or  replacement arguments are NULL. For backward compatibility reasons an exception is made
       for the replacement argument if the rlength argument is also 0.

       PCRE2_ERROR_BADREPLACEMENT is used for miscellaneous syntax errors in the replacement string,  with  more
       particular  errors  being PCRE2_ERROR_BADREPESCAPE (invalid escape sequence), PCRE2_ERROR_REPMISSINGBRACE
       (closing  curly  bracket  not  found),  PCRE2_ERROR_BADSUBSTITUTION  (syntax  error  in  extended   group
       substitution),  and  PCRE2_ERROR_BADSUBSPATTERN  (the  pattern match ended before it started or the match
       started earlier than the current position in  the  subject,  which  can  happen  if  \K  is  used  in  an
       assertion).

       As  for  all  PCRE2  errors,  a  text  message  that  describes  the error can be obtained by calling the
       pcre2_get_error_message() function (see "Obtaining a textual error message" above).

   Substitution callouts

       int pcre2_set_substitute_callout(pcre2_match_context *mcontext,
         int (*callout_function)(pcre2_substitute_callout_block *, void *),
         void *callout_data);

       The  pcre2_set_substitution_callout()  function  can  be  used  to  specify  a   callout   function   for
       pcre2_substitute().  This  information is passed in a match context. The callout function is called after
       each substitution has been processed, but it can cause the replacement not to happen.

       The callout function is  not  called  for  simulated  substitutions  that  happen  as  a  result  of  the
       PCRE2_SUBSTITUTE_OVERFLOW_LENGTH  option.  In  this mode, when substitution processing exceeds the buffer
       space provided by the caller, processing continues by counting code units. The simulation  is  unable  to
       populate  the  callout  block,  and  so  the  simulation  is  pessimistic about the required buffer size.
       Whichever is larger of accepted or rejected substitution is reported as the required size. Therefore, the
       returned  buffer  length  may be an overestimate (without a substitution callout, it is normally an exact
       measurement).

       The first argument of the callout function is a pointer to a substitute callout  block  structure,  which
       contains the following fields, not necessarily in this order:

         uint32_t    version;
         uint32_t    subscount;
         PCRE2_SPTR  input;
         PCRE2_SPTR  output;
         PCRE2_SIZE *ovector;
         uint32_t    oveccount;
         PCRE2_SIZE  output_offsets[2];

       The  version field contains the version number of the block format. The current version is 0. The version
       number will increase in future if more fields are added, but the intention is never to remove any of  the
       existing fields.

       The  subscount field is the number of the current match. It is 1 for the first callout, 2 for the second,
       and so on. The input and output pointers are copies of the values passed to pcre2_substitute().

       The ovector field points to the ovector, which  contains  the  result  of  the  most  recent  match.  The
       oveccount  field  contains  the  number  of pairs that are set in the ovector, and is always greater than
       zero.

       The output_offsets vector contains the offsets of the replacement in the output string. This has  already
       been processed for dollar and (if requested) backslash substitutions as described above.

       The  second  argument  of  the callout function is the value passed as callout_data when the function was
       registered. The value returned by the callout function is interpreted as follows:

       If the value is zero, the replacement is accepted, and, if  PCRE2_SUBSTITUTE_GLOBAL  is  set,  processing
       continues  with  a  search  for  the next match. If the value is not zero, the current replacement is not
       accepted. If the value is greater than zero, processing continues when  PCRE2_SUBSTITUTE_GLOBAL  is  set.
       Otherwise  (the  value is less than zero or PCRE2_SUBSTITUTE_GLOBAL is not set), the rest of the input is
       copied to the output and the call to pcre2_substitute() exits, returning the number of matches so far.

   Substitution case callouts

       int pcre2_set_substitute_case_callout(pcre2_match_context *mcontext,
         PCRE2_SIZE (*callout_function)(PCRE2_SPTR, PCRE2_SIZE,
                                        PCRE2_UCHAR *, PCRE2_SIZE,
                                        int, void *),
         void *callout_data);

       The pcre2_set_substitution_case_callout() function  can  be  used  to  specify  a  callout  function  for
       pcre2_substitute()  to  use  when  performing  case  transformations.  This  does  not  affect  any  case
       insensitivity behaviour when performing a match, but only the user-visible transformations performed when
       processing a substitution such as:

           pcre2_substitute(..., "\\U$1", ...)

       The  default  case  transformations  applied  by  PCRE2 are reasonably complete, and, in UTF or UCP mode,
       perform the simple locale-invariant case transformations as specified by Unicode. This  is  suitable  for
       the internal (invisible) case-equivalence procedures used during pattern matching, but an application may
       wish to use more sophisticated locale-aware processing for the user-visible substitution transformations.

       One example implementation of the callout_function using the ICU library would be:

           PCRE2_SIZE
           icu_case_callout(
             PCRE2_SPTR input, PCRE2_SIZE input_len,
             PCRE2_UCHAR *output, PCRE2_SIZE output_cap,
             int to_case, void *data_ptr)
           {
             UErrorCode err = U_ZERO_ERROR;
             int32_t r = to_case == PCRE2_SUBSTITUTE_CASE_LOWER
               ? u_strToLower(output, output_cap, input, input_len, NULL, &err)
               : to_case == PCRE2_SUBSTITUTE_CASE_UPPER
               ? u_strToUpper(output, output_cap, input, input_len, NULL, &err)
               : u_strToTitle(output, output_cap, input, input_len, &first_char_only,
                              NULL, &err);
             if (U_FAILURE(err)) return (~(PCRE2_SIZE)0);
             return r;
           }

       The first and second arguments of the case callout function are the Unicode string to transform.

       The third and fourth arguments are the output buffer and its capacity.

       The  fifth  is  one  of  the  constants  PCRE2_SUBSTITUTE_CASE_LOWER,   PCRE2_SUBSTITUTE_CASE_UPPER,   or
       PCRE2_SUBSTITUTE_CASE_TITLE_FIRST.    PCRE2_SUBSTITUTE_CASE_LOWER   and  PCRE2_SUBSTITUTE_CASE_UPPER  are
       passed to the callout to indicate that the case of the entire callout input should  be  case-transformed.
       PCRE2_SUBSTITUTE_CASE_TITLE_FIRST  is passed to indicate that only the first character or glyph should be
       transformed to Unicode titlecase and the rest to Unicode lowercase (note that titlecasing sometimes  uses
       Unicode  properties  to  titlecase  each  word  in a string; but PCRE2 is requesting that only the single
       leading character is to be titlecased).

       The sixth argument is the callout_data supplied to pcre2_set_substitute_case_callout().

       The resulting string in the destination buffer may be larger or smaller than the  input,  if  the  casing
       rules  merge  or  split  characters.  The return value is the length required for the output string. If a
       buffer of sufficient size was provided to the callout, then the result must be written to the buffer  and
       the  number  of code units returned. If the result does not fit in the provided buffer, then the required
       capacity must be returned and PCRE2 will not make use of the output  buffer.  PCRE2  provides  input  and
       output buffers which overlap, so the callout must support this by suitable internal buffering.

       Alternatively,  if  the callout wishes to indicate an error, then it may return (~(PCRE2_SIZE)0). In this
       case pcre2_substitute() will immediately fail with error PCRE2_ERROR_REPLACECASE.

       When a case callout is combined with the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option,  there  are  situations
       when  pcre2_substitute()  will  return  an  underestimate  of  the  required  buffer  size.  If  you call
       pcre2_substitute() once with PCRE2_SUBSTITUTE_OVERFLOW_LENGTH, and the input buffer is too small for  the
       replacement  string  to be constructed, then instead of calling the case callout, pcre2_substitute() will
       make   an   estimate   of   the   required   buffer   size.    The   second   call   should   also   pass
       PCRE2_SUBSTITUTE_OVERFLOW_LENGTH,  because  that  second call is not guaranteed to succeed either, if the
       case callout requires more buffer space than expected. The caller must make repeated attempts in a loop.

DUPLICATE CAPTURE GROUP NAMES

       int pcre2_substring_nametable_scan(const pcre2_code *code,
         PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);

       When a pattern is compiled with the PCRE2_DUPNAMES option, names for capture groups are not  required  to
       be  unique.  Duplicate names are always allowed for groups with the same number, created by using the (?|
       feature. Indeed, if such groups are named, they are required to use the same names.

       Normally, patterns that use duplicate names are such that in any one match,  only  one  of  each  set  of
       identically-named groups participates. An example is shown in the pcre2pattern documentation.

       When  duplicates  are  present, pcre2_substring_copy_byname() and pcre2_substring_get_byname() return the
       first substring corresponding to the given name that is set. Only if none are set is PCRE2_ERROR_UNSET is
       returned. The pcre2_substring_number_from_name() function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING
       when there are duplicate names.

       If you want to get full details  of  all  captured  substrings  for  a  given  name,  you  must  use  the
       pcre2_substring_nametable_scan()  function. The first argument is the compiled pattern, and the second is
       the name. If the third and fourth arguments are NULL, the function returns a group number  for  a  unique
       name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.

       When  the third and fourth arguments are not NULL, they must be pointers to variables that are updated by
       the function. After it has run, they point to the first and last entries in the name-to-number table  for
       the  given  name,  and  the  function  returns  the  length  of  each entry in code units. In both cases,
       PCRE2_ERROR_NOSUBSTRING is returned if there are no entries for the given name.

       The format of the name table is described above in the section  entitled  Information  about  a  pattern.
       Given  all  the  relevant  entries  for  the  name,  you can extract each of their numbers, and hence the
       captured data.

FINDING ALL POSSIBLE MATCHES AT ONE POSITION

       The traditional matching function uses a similar algorithm to Perl, which stops when it finds  the  first
       match  at a given point in the subject. If you want to find all possible matches, or the longest possible
       match at a given position, consider using the alternative matching function (see below) instead.  If  you
       cannot use the alternative function, you can kludge it up by making use of the callout facility, which is
       described in the pcre2callout documentation.

       What you have to do is to insert a callout right at the end of the pattern.  When your  callout  function
       is  called,  extract and save the current matched substring. Then return 1, which forces pcre2_match() to
       backtrack and try other alternatives. Ultimately, when it runs out of matches, pcre2_match()  will  yield
       PCRE2_ERROR_NOMATCH.

MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

       int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
         PCRE2_SIZE length, PCRE2_SIZE startoffset,
         uint32_t options, pcre2_match_data *match_data,
         pcre2_match_context *mcontext,
         int *workspace, PCRE2_SIZE wscount);

       The  function  pcre2_dfa_match()  is called to match a subject string against a compiled pattern, using a
       matching algorithm that scans the subject string just once (not counting lookaround assertions), and does
       not  backtrack  (except when processing lookaround assertions). This has different characteristics to the
       normal algorithm, and is not compatible with Perl. Some  of  the  features  of  PCRE2  patterns  are  not
       supported.  Nevertheless,  there  are times when this kind of matching can be useful. For a discussion of
       the two matching algorithms, and a list of features that pcre2_dfa_match()  does  not  support,  see  the
       pcre2matching documentation.

       The  arguments for the pcre2_dfa_match() function are the same as for pcre2_match(), plus two extras. The
       ovector within the match data block is used in a different way, and this is described  below.  The  other
       common  arguments  are  used  in  the same way as for pcre2_match(), so their description is not repeated
       here.

       The two additional arguments provide workspace for the function. The workspace vector should  contain  at
       least  20  elements.  It  is  used  for  keeping  track  of multiple paths through the pattern tree. More
       workspace is needed for patterns and subjects where there are a lot of potential matches.

       Here is an example of a simple call to pcre2_dfa_match():

         int wspace[20];
         pcre2_match_data *md = pcre2_match_data_create(4, NULL);
         int rc = pcre2_dfa_match(
           re,             /* result of pcre2_compile() */
           "some string",  /* the subject string */
           11,             /* the length of the subject string */
           0,              /* start at offset 0 in the subject */
           0,              /* default options */
           md,             /* the match data block */
           NULL,           /* a match context; NULL means use defaults */
           wspace,         /* working space vector */
           20);            /* number of elements (NOT size in bytes) */

   Option bits for pcre2_dfa_match()

       The unused bits of the options argument for pcre2_dfa_match() must be zero. The only bits that may be set
       are    PCRE2_ANCHORED,   PCRE2_COPY_MATCHED_SUBJECT,   PCRE2_ENDANCHORED,   PCRE2_NOTBOL,   PCRE2_NOTEOL,
       PCRE2_NOTEMPTY,  PCRE2_NOTEMPTY_ATSTART,  PCRE2_NO_UTF_CHECK,   PCRE2_PARTIAL_HARD,   PCRE2_PARTIAL_SOFT,
       PCRE2_DFA_SHORTEST,  and  PCRE2_DFA_RESTART.  All  but the last four of these are exactly the same as for
       pcre2_match(), so their description is not repeated here.

         PCRE2_PARTIAL_HARD
         PCRE2_PARTIAL_SOFT

       These have the same general effect as they do for pcre2_match(), but the details are slightly  different.
       When  PCRE2_PARTIAL_HARD  is  set for pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of the
       subject is reached and there is  still  at  least  one  matching  possibility  that  requires  additional
       characters.  This  happens even if some complete matches have already been found. When PCRE2_PARTIAL_SOFT
       is set, the return code PCRE2_ERROR_NOMATCH is converted into  PCRE2_ERROR_PARTIAL  if  the  end  of  the
       subject  is  reached,  there  have  been  no  complete  matches, but there is still at least one matching
       possibility. The portion of the string that was inspected when the longest partial match was found is set
       as  the  first  matching  string in both cases. There is a more detailed discussion of partial and multi-
       segment matching, with examples, in the pcre2partial documentation.

         PCRE2_DFA_SHORTEST

       Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to stop as soon as it has  found  one
       match.  Because  of  the  way  the alternative algorithm works, this is necessarily the shortest possible
       match at the first possible matching point in the subject string.

         PCRE2_DFA_RESTART

       When pcre2_dfa_match() returns a partial match, it is possible to call it again, with additional  subject
       characters,  and have it continue with the same match. The PCRE2_DFA_RESTART option requests this action;
       when it is set, the workspace and wscount options must reference the same vector as before  because  data
       about  the  match so far is left in them after a partial match. There is more discussion of this facility
       in the pcre2partial documentation.

   Successful returns from pcre2_dfa_match()

       When pcre2_dfa_match() succeeds, it may have matched more  than  one  substring  in  the  subject.  Note,
       however,  that  all  the matches from one run of the function start at the same point in the subject. The
       shorter matches are all initial substrings of the longer matches. For example, if the pattern

         <.*>

       is matched against the string

         This is <something> <something else> <something further> no more

       the three matched strings are

         <something> <something else> <something further>
         <something> <something else>
         <something>

       On success, the yield of the function is a number greater than zero,  which  is  the  number  of  matched
       substrings.  The offsets of the substrings are returned in the ovector, and can be extracted by number in
       the same way as for pcre2_match(), but the numbers bear no relation to any capture groups that may  exist
       in the pattern, because DFA matching does not support capturing.

       Calls to the convenience functions that extract substrings by name return the error PCRE2_ERROR_DFA_UFUNC
       (unsupported function) if used after a DFA match. The convenience functions that  extract  substrings  by
       number never return PCRE2_ERROR_NOSUBSTRING.

       The  matched  strings are stored in the ovector in reverse order of length; that is, the longest matching
       string is first. If there were too many matches to fit into the ovector, the yield  of  the  function  is
       zero, and the vector is filled with the longest matches.

       NOTE:  PCRE2's  "auto-possessification" optimization usually applies to character repeats at the end of a
       pattern (as well as internally). For example, the pattern "a\d+" is compiled as if it were  "a\d++".  For
       DFA matching, this means that only one possible match is found. If you really do want multiple matches in
       such cases, either use an ungreedy repeat such as "a\d+?" or set the  PCRE2_NO_AUTO_POSSESS  option  when
       compiling.

   Error returns from pcre2_dfa_match()

       The  pcre2_dfa_match() function returns a negative number when it fails.  Many of the errors are the same
       as for pcre2_match(), as described above.  There are in addition the following errors that  are  specific
       to pcre2_dfa_match():

         PCRE2_ERROR_DFA_UITEM

       This return is given if pcre2_dfa_match() encounters an item in the pattern that it does not support, for
       instance, the use of \C in a UTF mode or a backreference.

         PCRE2_ERROR_DFA_UCOND

       This return is given if pcre2_dfa_match() encounters a condition item that uses a backreference  for  the
       condition, or a test for recursion in a specific capture group. These are not supported.

         PCRE2_ERROR_DFA_UINVALID_UTF

       This   return   is   given  if  pcre2_dfa_match()  is  called  for  a  pattern  that  was  compiled  with
       PCRE2_MATCH_INVALID_UTF. This is not supported for DFA matching.

         PCRE2_ERROR_DFA_WSSIZE

       This return is given if pcre2_dfa_match() runs out of space in the workspace vector.

         PCRE2_ERROR_DFA_RECURSE

       When a recursion or subroutine call is processed, the matching function calls itself  recursively,  using
       private  memory  for the ovector and workspace.  This error is given if the internal ovector is not large
       enough. This should be extremely rare, as a vector of size 1000 is used.

         PCRE2_ERROR_DFA_BADRESTART

       When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option, some plausibility checks are made  on
       the  contents  of  the  workspace,  which should contain data about the previous partial match. If any of
       these checks fail, this error is given.

SEE ALSO

       pcre2build(3),   pcre2callout(3),   pcre2demo(3),   pcre2matching(3),   pcre2partial(3),   pcre2posix(3),
       pcre2sample(3), pcre2unicode(3).

AUTHOR

       Philip Hazel
       Retired from University Computing Service
       Cambridge, England.

REVISION

       Last updated: 26 December 2024
       Copyright (c) 1997-2024 University of Cambridge.