NAME

       PCRE2 - Perl-compatible regular expressions (revised API)

SIZE AND OTHER LIMITATIONS

       There  are some size limitations in PCRE2 but it is hoped that they will never in practice
       be relevant.

       The maximum size of a compiled pattern is approximately 64 thousand  code  units  for  the
       8-bit  and  16-bit  libraries if PCRE2 is compiled with the default internal linkage size,
       which is 2 bytes for these libraries. If you want to process regular expressions that  are
       truly  enormous,  you  can  compile  PCRE2  with  an internal linkage size of 3 or 4 (when
       building the 16-bit library, 3 is rounded up to 4). See the  README  file  in  the  source
       distribution  and  the  pcre2build  documentation for details. In these cases the limit is
       substantially larger.  However, the speed of execution is slower. In the  32-bit  library,
       the internal linkage size is always 4.

       The  maximum length of a source pattern string is essentially unlimited; it is the largest
       number a PCRE2_SIZE variable can hold. However, the program that calls pcre2_compile() can
       specify a smaller limit.

       The maximum length (in code units) of a subject string is one less than the largest number
       a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned integer type, usually defined as
       size_t.  Its maximum value (that is ~(PCRE2_SIZE)0) is reserved as a special indicator for
       zero-terminated strings and unset offsets.

       All values in repeating quantifiers must be less than 65536.

       The maximum length of a lookbehind assertion is 65535 characters.

       There is no limit to the number of parenthesized groups, but there can  be  no  more  than
       65535  capture  groups,  and  there  is  a  limit to the depth of nesting of parenthesized
       subpatterns of all kinds. This is imposed in order to limit the  amount  of  system  stack
       used  at compile time. The default limit can be specified when PCRE2 is built; if not, the
       default  is  set  to  250.   An   application   can   change   this   limit   by   calling
       pcre2_set_parens_nest_limit() to set the limit in a compile context.

       The  maximum  length  of  name for a named capture group is 32 code units, and the maximum
       number of such groups is 10000.

       The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb is 255  code
       units for the 8-bit library and 65535 code units for the 16-bit and 32-bit libraries.

       The  maximum  length  of  a  string  argument  to a callout is the largest number a 32-bit
       unsigned integer can hold.

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge, England.

REVISION

       Last updated: 02 February 2019
       Copyright (c) 1997-2019 University of Cambridge.