Ubuntu Manpage: XML::Easy::Syntax - excruciatingly correct XML syntax

Provided by: libxml-easy-perl_0.009-1build1_amd64

NAME

       XML::Easy::Syntax - excruciatingly correct XML syntax

SYNOPSIS

               use XML::Easy::Syntax qw($xml10_name_rx);
               if($name =~ /\A$xml10_name_rx\z/o) { ...
               # and many other regular expressions

DESCRIPTION

       This module supplies Perl regular expressions describing the grammar of XML 1.0.  This is intended to
       support doing irregular things with XML, rather than for normal parsing.

       These regular expressions encompass the entire XML grammar except for document type declarations and
       DTDs.  This document assumes general familiarity with XML.

REGULAR EXPRESSIONS

Each of these regular expressions corresponds precisely to one of the productions in the EBNF grammar in
the XML 1.0 specification. Well-formedness constraints that are not expressed in the EBNF are not
checked by the regular expressions; these are noted in the documentation below. The regular expressions
do not include any anchors, so to check whether an entire string matches a production you must supply the
anchors yourself.

Syntax pieces
$xml10_char_rx
Any single character that is acceptable to XML 1.0. This includes most Unicode characters (up to
codepoint 0x10ffff). The excluded codepoints are the sentinels 0xfffe and 0xffff, the surrogate
blocks, and most of the C0 control characters (0x00 to 0x1f, except for 0x09 (tab), 0x0a
(linefeed/newline), and 0x0d (carriage return)).

It is a rule of XML that all characters making up an XML document must be in this permitted set. The
grammar productions can only match sequences of acceptable characters. This rule is enforced by the
regular expressions in this module.

Furthermore, it is a rule that the character data in a document cannot even represent a character
outside the permitted set. This is expressed as a well-formedness constraint on character
references.

$xml10_s_rx
Any sequence of one or more acceptable whitespace characters. The whitespace characters, for this
purpose, are tab, linefeed/newline, carriage return, and space. Non-ASCII whitespace characters, and
the more exotic ASCII whitespace characters, do not qualify.

$xml10_eq_rx
Equals sign, surrounded by optional whitespace.

Names
$xml10_namestartchar_rx
Any single character that is permitted at the start of a name. The permitted characters are "_",
":", and letters (categorised according to Unicode 2.0).

This production is not named in the XML specification.

$xml10_namechar_rx
Any single character that is permitted in a name other than at the start. The permitted characters
are ".", "-", "_", ":", and letters, digits, combining characters, and extenders (categorised
according to Unicode 2.0).

$xml10_name_rx
A name, of the type used to identify element types, attributes, entities, and other things in XML.

$xml10_names_rx
A space-separated list of one or more names.

$xml10_nmtoken_rx
A name-like token, much like a name except that the first character is no more restricted than the
remaining characters. These tokens play no part in basic XML syntax, and in the specification are
only used as part of attribute typing.

$xml10_nmtokens_rx
A space-separated list of one or more name-like tokens.

References
$xml10_charref_rx
A numeric character reference (beginning with "&#" and ending with ";"). There is a non-syntactic
well-formedness constraint: the codepoint is required to be within the Unicode range and to refer to
an acceptable character (as discussed at $xml10_char_rx).

$xml10_entityref_rx
A general entity reference (beginning with "&" and ending with ";"). There are non-syntactic well-
formedness constraints: the referenced entity must be declared (possibly implicitly), must not be an
unparsed entity, must not contain a recursive reference to itself, and its replacement text must
itself be well-formed.

$xml10_reference_rx
Either a character reference or an entity reference. The well-formedness constraints of both
reference types (see above) apply.

Character data
$xml10_chardata_rx
Ordinary literal character data. This consists of zero or more acceptable charaters, other than the
metacharacters "<" and "&", and not including "]]>" as a subsequence. Such data stands for itself
when it appears between the start and end tags of an element, where it can be interspersed with
references, CDATA sections, comments, and processing instructions.

In the XML grammar, character data is parsed, and taken literally, after line endings have been
canonicalised (to the newline character). Pre-canonicalisation character data, with variable line
endings, will still match this production but should not be interpreted literally.

Beware that a string that does not match this production might parse as two adjacent strings each of
which matches. This can happen because of the prohibition on "]]>" being embedded in character data,
while the characters of that sequence are acceptable individually. The XML grammar does not allow
two instances of this production to abut.

$xml10_cdata_rx
Literal character data in a CDATA section. This consists of zero or more acceptable charaters, not
including "]]>" as a subsequence. Unlike ordinary literal character data, the characters "<" and "&"
are not metacharacters here. Such data stands for itself when it appears within a CDATA section.

As with ordinary literal character data (see above), this data is meant to be taken literally only
after line endings have been canonicalised. Also, as with ordinary literal character data, two
instances of this production should not abut.

$xml10_cdstart_rx
$xml10_cdend_rx
The fixed strings "<![CDATA[" and "]]>" which begin and finish a CDATA section.

$xml10_cdsect_rx
A CDATA section. This consists of "<![CDATA[", literal character data with metacharacters disabled,
and "]]>".

Tags
$xml10_attvalue_rx
A quoted attribute value. This consists of acceptable characters other than "<", "&", and the quote
character, interspersed with references, surrounded by matching """ or "'" quotes. The well-
formedness constraints of references apply, and additionally the replacement text of any referenced
entities must not contain any "<" characters, and it is not permitted to refer to external entities.

$xml10_attribute_rx
A complete attribute, consisting of name, equals sign, and quoted value. The well-formedness
constraints of attribute values (pertaining to references) apply.

$xml10_stag_rx
A start-tag, used to begin an element. This consists of "<", the element type name, whitespace-
separated list of attributes, and ">". The well-formedness constraints of attribute values
(pertaining to references) apply. There is also a well-formedness constraint that attribute names
must be unique within the tag.

$xml10_etag_rx
An end-tag, used to finish an element. This consists of "</", the element type name, and ">".

$xml10_emptyelemtag_rx
An empty-element tag, used to represent an element with no content. This consists of "<", the
element type name, whitespace-separated list of attributes, and "/>". The well-formedness
constraints of attribute values (pertaining to references) apply. There is also a well-formedness
constraint that attribute names must be unique within the tag. (These are the same constraints as
for start-tags.)

Non-data content
$xml10_comment_rx
A comment. This does not contribute to the data content of an XML document. It consists of "". It is not permitted for the content to include "--"
as a subsequence, nor for it to end with "-".

$xml10_pitarget_rx
A processing instruction target name. This can be any name (the $xml10_name_rx production) except
for "xml" and its case variations.

$xml10_pi_rx
A processing instruction. This consists of "<?", a target name, some content which can be almost any
sequence of acceptable characters, and "?>". A processing instruction does not contribute to the
data content of an XML document, but is intended to carry metadata regarding how to process it. The
instruction is addressed to a particular XML processor, or type of processor, identified by the
target name, and the content of the instruction is expected to be meaningful only to its target.

No one has ever come up with a good use for processing instructions. They are best shunned.

Recursive structure
$xml10_content_rx
The matter contained within an element (between its start-tag and end-tag). This consists of
stretches of ordinary literal character data, interspersed with complete elements (recursively),
references, CDATA sections, processing instructions, and comments, in any order. The well-formedness
constraints of references and elements apply.

$xml10_element_rx
A complete element. This is either an empty-element tag, or a sequence of start-tag, content, and
end-tag. The well-formedness constraints regarding references and attribute uniqueness apply in the
empty-element tag or start-tag. In the non-empty form, the content also has well-formedness
constraints regarding references and (recursively) contained elements, and there is an additional
constraint that the element type name in the end-tag must match that in the start-tag.

XML declarations
$xml10_versionnum_rx
The version number of the XML specification. This is the fixed string "1.0".

$xml10_versioninfo_rx
The version declaration part of an XML declaration.

$xml10_encname_rx
A character encoding name. This must start with an ASCII letter, and contain only ASCII letters and
digits and ".", "_", and "-".

$xml10_encodingdecl_rx
The encoding declaration part of an XML declaration.

$xml10_sddecl_rx
The standaloneness declaration part of an XML declaration. This indicates whether the XML document
can be correctly interpreted without examining the external part of the DTD.

$xml10_xmldecl_rx
An XML declaration, as used at the start of an XML document. This consists of "<?xml", mandatory
version declaration, optional encoding declaration, optional standaloneness declaration, and "?>".

$xml10_textdecl_rx
A text declaration, as used at the start of an XML external parsed entity or external DTD. This
consists of "<?xml", optional version declaration, mandatory encoding declaration, and "?>". This is
very similar to an XML declaration, but technically a different item and used in different
situations. It is possible, and useful, to construct a declaration which is acceptable both as an
XML declaration and as a text declaration.

Document structure
$xml10_misc_rx
Non-content item permitted in the prologue and epilogue of a document. This is either a comment, a
processing instruction, or a stretch of whitespace.

Beware in using a pattern such as "$xml10_misc_rx*". It could match a string of whitespace charaters
in many ways, leading to exponential behaviour if it becomes necessary to backtrack. This can be
avoided by using the $xml10_miscseq_rx pattern (below).

$xml10_miscseq_rx
A sequence (possibly empty) of non-content matter permitted in the prologue and epilogue of a
document. This can contain comments, processing instructions, and whitespace, in any order.

This production is not named in the XML specification. This regular expression should be preferred
over "$xml10_misc_rx*" (which is the direct translation of what appears in the XML specification),
because this one guarantees to match a particular text in only one way, and is thus able to backtrack
cleanly.

$xml10_prolog_xdtd_rx
Document prologue, except for not permitting a document type declaration. This consists of an
optional XML declaration followed by any sequence of comments, processing instructions, and
whitespace.

$xml10_document_xdtd_rx
A complete XML document, except for not permitting a document type declaration. This consists of a
non-content prologue, an element (the root element, which can recursively contain other elements),
and a non-content epilogue. The well-formedness constraints of elements apply to the root element.

$xml10_extparsedent_rx
A complete external parsed entity. This consists of an optional text declaration followed by a
sequence of content of the same type that is permitted within an element. The well-formedness
constraints of element content apply.

BUGS

       Many of these regular expressions are liable to tickle a serious bug in perl's regexp engine.  The bug is
       that the "*" and "+" repeat operators don't always match an unlimited number of repeats:  in  some  cases
       they  are limited to 32767 iterations.  Whether this bogus limit applies depends on the complexity of the
       expression being repeated, whether the string being examined is internally  encoded  in  UTF-8,  and  the
       version  of  perl.   In  some cases, but not all, a false match failure is preceded by a warning "Complex
       regular subexpression recursion limit (32766) exceeded".

       This bug is present, in various forms, in all perl versions up to at least 5.8.9  and  5.10.0.   Pre-5.10
       perls may also overflow their stack space, in similar circumstances, if a resource limit is imposed.

       There is no known feasible workaround for this perl bug.  The regular expressions supplied by this module
       will  therefore, unavoidably, fail to accept some lengthy valid inputs.  Where this occurs, though, it is
       likely that other regular expressions being applied to the same or related input  will  also  suffer  the
       same  problem.  It is pervasive.  Do not rely on this module (or perl) to process long inputs on affected
       perl versions.

       This bug does not affect the XML::Easy::Text parser.

AUTHOR

       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

       Copyright (C) 2008, 2009 PhotoBox Ltd

       Copyright (C) 2009, 2010, 2011 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This module is free software; you can redistribute it and/or modify it  under  the  same  terms  as  Perl
       itself.

perl v5.18.1                                       2013-10-22                             XML::Easy::Syntax(3pm)