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Updates to the README and some documentation (#681)

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Nicholas Wilson
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@@ -50,7 +50,7 @@ please consult the man page, in case the conversion went wrong.
<li><a name="TOC35" href="#SEC35">REVISION</a>
</ul>
<br><a name="SEC1" href="#TOC1">PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY</a><br>
<P>
<p>
The full syntax and semantics of the regular expression patterns that are
supported by PCRE2 are described in the
<a href="pcre2pattern.html"><b>pcre2pattern</b></a>
@@ -59,9 +59,9 @@ syntax followed by the syntax of replacement strings in substitution function.
The full description of the latter is in the
<a href="pcre2api.html"><b>pcre2api</b></a>
documentation.
</P>
</p>
<br><a name="SEC2" href="#TOC1">QUOTING</a><br>
<P>
<p>
<pre>
\x where x is non-alphanumeric is a literal x
\Q...\E treat enclosed characters as literal
@@ -71,9 +71,9 @@ PCRE2_EXTENDED is set, causing most other white space to be ignored. Note also
that PCRE2's handling of \Q...\E has some differences from Perl's. See the
<a href="pcre2pattern.html"><b>pcre2pattern</b></a>
documentation for details.
</P>
</p>
<br><a name="SEC3" href="#TOC1">BRACED ITEMS</a><br>
<P>
<p>
With one exception, wherever brace characters { and } are required to enclose
data for constructions such as \g{2} or \k{name}, space and/or horizontal tab
characters that follow { or precede } are allowed and are ignored. In the case
@@ -81,9 +81,9 @@ of quantifiers, they may also appear before or after the comma. The exception
is \u{...} which is not Perl-compatible and is recognized only when
PCRE2_EXTRA_ALT_BSUX is set. This is an ECMAScript compatibility feature, and
follows ECMAScript's behaviour.
</P>
</p>
<br><a name="SEC4" href="#TOC1">ESCAPED CHARACTERS</a><br>
<P>
<p>
This table applies to ASCII and Unicode environments. An unrecognized escape
sequence causes an error.
<pre>
@@ -104,8 +104,8 @@ sequence causes an error.
\N{U+hh..} is synonymous with \x{hh..} but is not supported in environments
that use EBCDIC code (mainly IBM mainframes). Note that \N not followed by an
opening curly bracket has a different meaning (see below).
</P>
<P>
</p>
<p>
If PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX is set ("ALT_BSUX mode"), the
following are also recognized:
<pre>
@@ -119,8 +119,8 @@ recognized as a hexadecimal escape; otherwise it matches a literal "x".
Likewise, if \u (in ALT_BSUX mode) is not followed by four hexadecimal digits
or (in EXTRA_ALT_BSUX mode) a sequence of hex digits in curly brackets, it
matches a literal "u".
</P>
<P>
</p>
<p>
Note that \0dd is always an octal code. The treatment of backslash followed by
a non-zero digit is complicated; for details see the section
<a href="pcre2pattern.html#digitsafterbackslash">"Non-printing characters"</a>
@@ -128,9 +128,9 @@ in the
<a href="pcre2pattern.html"><b>pcre2pattern</b></a>
documentation, where details of escape processing in EBCDIC environments are
also given.
</P>
</p>
<br><a name="SEC5" href="#TOC1">CHARACTER TYPES</a><br>
<P>
<p>
<pre>
. any character except newline;
in dotall mode, any character whatsoever
@@ -155,8 +155,8 @@ also given.
of a UTF-8 or UTF-16 character. The application can lock out the use of \C by
setting the PCRE2_NEVER_BACKSLASH_C option. It is also possible to build PCRE2
with the use of \C permanently disabled.
</P>
<P>
</p>
<p>
By default, \d, \s, and \w match only ASCII characters, even in UTF-8 mode
or in the 16-bit and 32-bit libraries. However, if locale-specific matching is
happening, \s and \w may also match characters with code points in the range
@@ -164,15 +164,15 @@ happening, \s and \w may also match characters with code points in the range
sequences is changed to use Unicode properties and they match many more
characters, but there are some option settings that can restrict individual
sequences to matching only ASCII characters.
</P>
<P>
</p>
<p>
Property descriptions in \p and \P are matched caselessly; hyphens,
underscores, and ASCII white space characters are ignored, in accordance with
Unicode's "loose matching" rules. For example, \p{Bidi_Class=al} is the same
as \p{ bidi class = AL }.
</P>
</p>
<br><a name="SEC6" href="#TOC1">GENERAL CATEGORY PROPERTIES FOR \p and \P</a><br>
<P>
<p>
<pre>
C Other
Cc Control
@@ -222,9 +222,9 @@ as \p{ bidi class = AL }.
</pre>
From release 10.45, when caseless matching is set, Ll, Lu, and Lt are all
equivalent to Lc.
</P>
</p>
<br><a name="SEC7" href="#TOC1">PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P</a><br>
<P>
<p>
<pre>
Xan Alphanumeric: union of properties L and N
Xps POSIX space: property Z or tab, NL, VT, FF, CR
@@ -235,27 +235,27 @@ equivalent to Lc.
</pre>
Perl and POSIX space are now the same. Perl added VT to its space character set
at release 5.18.
</P>
</p>
<br><a name="SEC8" href="#TOC1">BINARY PROPERTIES FOR \p AND \P</a><br>
<P>
<p>
Unicode defines a number of binary properties, that is, properties whose only
values are true or false. You can obtain a list of those that are recognized by
\p and \P, along with their abbreviations, by running this command:
<pre>
pcre2test -LP
</PRE>
</P>
</pre>
</p>
<br><a name="SEC9" href="#TOC1">SCRIPT MATCHING WITH \p AND \P</a><br>
<P>
<p>
Many script names and their 4-letter abbreviations are recognized in
\p{sc:...} or \p{scx:...} items, or on their own with \p (and also \P of
course). You can obtain a list of these scripts by running this command:
<pre>
pcre2test -LS
</PRE>
</P>
</pre>
</p>
<br><a name="SEC10" href="#TOC1">THE BIDI_CLASS PROPERTY FOR \p AND \P</a><br>
<P>
<p>
<pre>
\p{Bidi_Class:&#60;class&#62;} matches a character with the given class
\p{BC:&#60;class&#62;} matches a character with the given class
@@ -285,10 +285,10 @@ The recognized classes are:
RLO right-to-left override
S segment separator
WS white space
</PRE>
</P>
</pre>
</p>
<br><a name="SEC11" href="#TOC1">CHARACTER CLASSES</a><br>
<P>
<p>
<pre>
[...] positive character class
[^...] negative character class
@@ -314,8 +314,8 @@ The recognized classes are:
In PCRE2, POSIX character set names recognize only ASCII characters by default,
but some of them use Unicode properties if PCRE2_UCP is set. You can use
\Q...\E inside a character class.
</P>
<P>
</p>
<p>
When PCRE2_ALT_EXTENDED_CLASS is set, UTS#18 extended character classes may be
used, allowing nested character classes, combined using set operators.
<pre>
@@ -326,10 +326,10 @@ used, allowing nested character classes, combined using set operators.
x--y set difference (AND NOT)
x~~y set symmetric difference (XOR)
</PRE>
</P>
</pre>
</p>
<br><a name="SEC12" href="#TOC1">PERL EXTENDED CHARACTER CLASSES</a><br>
<P>
<p>
<pre>
(?[...]) Perl extended character class
(?[\p{Thai} & \p{Nd}]) operators; whitespace ignored
@@ -352,9 +352,9 @@ as an ordinary character class. Outside of a nested [...], the only items
permitted are backslash-escapes, POSIX sets, operators, and parentheses. Inside
a nested ordinary class, ^ has its usual meaning (inverts the class when used
as the first character); outside of a nested class, ^ is the XOR operator.
</P>
</p>
<br><a name="SEC13" href="#TOC1">QUANTIFIERS</a><br>
<P>
<p>
<pre>
? 0 or 1, greedy
?+ 0 or 1, possessive
@@ -375,10 +375,10 @@ as the first character); outside of a nested class, ^ is the XOR operator.
{,m} zero up to m, greedy
{,m}+ zero up to m, possessive
{,m}? zero up to m, lazy
</PRE>
</P>
</pre>
</p>
<br><a name="SEC14" href="#TOC1">ANCHORS AND SIMPLE ASSERTIONS</a><br>
<P>
<p>
<pre>
\b word boundary
\B not a word boundary
@@ -393,10 +393,10 @@ as the first character); outside of a nested class, ^ is the XOR operator.
also before newline at end of subject
\z end of subject
\G first matching position in subject
</PRE>
</P>
</pre>
</p>
<br><a name="SEC15" href="#TOC1">REPORTED MATCH POINT SETTING</a><br>
<P>
<p>
<pre>
\K set reported start of match
</pre>
@@ -404,15 +404,15 @@ From release 10.38 \K is not permitted by default in lookaround assertions,
for compatibility with Perl. However, if the PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK
option is set, the previous behaviour is re-enabled. When this option is set,
\K is honoured in positive assertions, but ignored in negative ones.
</P>
</p>
<br><a name="SEC16" href="#TOC1">ALTERNATION</a><br>
<P>
<p>
<pre>
expr|expr|expr...
</PRE>
</P>
</pre>
</p>
<br><a name="SEC17" href="#TOC1">CAPTURING</a><br>
<P>
<p>
<pre>
(...) capture group
(?&#60;name&#62;...) named capture group (Perl)
@@ -425,22 +425,22 @@ option is set, the previous behaviour is re-enabled. When this option is set,
In non-UTF modes, names may contain underscores and ASCII letters and digits;
in UTF modes, any Unicode letters and Unicode decimal digits are permitted. In
both cases, a name must not start with a digit.
</P>
</p>
<br><a name="SEC18" href="#TOC1">ATOMIC GROUPS</a><br>
<P>
<p>
<pre>
(?&#62;...) atomic non-capture group
(*atomic:...) atomic non-capture group
</PRE>
</P>
</pre>
</p>
<br><a name="SEC19" href="#TOC1">COMMENT</a><br>
<P>
<p>
<pre>
(?#....) comment (not nestable)
</PRE>
</P>
</pre>
</p>
<br><a name="SEC20" href="#TOC1">OPTION SETTING</a><br>
<P>
<p>
Changes of these options within a group are automatically cancelled at the end
of the group.
<pre>
@@ -465,15 +465,15 @@ of the group.
(?aP) implies (?aT) as well, though this has no additional effect. However, it
means that (?-aP) also implies (?-aT) and disables all ASCII restrictions for
POSIX classes.
</P>
<P>
</p>
<p>
Unsetting x or xx unsets both. Several options may be set at once, and a
mixture of setting and unsetting such as (?i-x) is allowed, but there may be
only one hyphen. Setting (but no unsetting) is allowed after (?^ for example
(?^in). An option setting may appear at the start of a non-capture group, for
example (?i:...).
</P>
<P>
</p>
<p>
The following are recognized only at the very start of a pattern or after one
of the newline or \R sequences or options with similar syntax. More than one
of them may appear. For the first three, d is a decimal number.
@@ -497,9 +497,9 @@ the limits set by the caller of <b>pcre2_match()</b> or <b>pcre2_dfa_match()</b>
not increase them. LIMIT_RECURSION is an obsolete synonym for LIMIT_DEPTH. The
application can lock out the use of (*UTF) and (*UCP) by setting the
PCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, respectively, at compile time.
</P>
</p>
<br><a name="SEC21" href="#TOC1">NEWLINE CONVENTION</a><br>
<P>
<p>
These are recognized only at the very start of the pattern or after option
settings with a similar syntax.
<pre>
@@ -509,19 +509,19 @@ settings with a similar syntax.
(*ANYCRLF) all three of the above
(*ANY) any Unicode newline sequence
(*NUL) the NUL character (binary zero)
</PRE>
</P>
</pre>
</p>
<br><a name="SEC22" href="#TOC1">WHAT \R MATCHES</a><br>
<P>
<p>
These are recognized only at the very start of the pattern or after option
setting with a similar syntax.
<pre>
(*BSR_ANYCRLF) CR, LF, or CRLF
(*BSR_UNICODE) any Unicode newline sequence
</PRE>
</P>
</pre>
</p>
<br><a name="SEC23" href="#TOC1">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a><br>
<P>
<p>
<pre>
(?=...) )
(*pla:...) ) positive lookahead
@@ -545,9 +545,9 @@ the maximum for each branch is limited to a value set by the caller of
<b>pcre2_compile()</b> or defaulted. The default is set when PCRE2 is built
(ultimate default 255). If every branch matches a fixed number of characters,
the limit for each branch is 65535 characters.
</P>
</p>
<br><a name="SEC24" href="#TOC1">NON-ATOMIC LOOKAROUND ASSERTIONS</a><br>
<P>
<p>
These assertions are specific to PCRE2 and are not Perl-compatible.
<pre>
(?*...) )
@@ -557,10 +557,10 @@ These assertions are specific to PCRE2 and are not Perl-compatible.
(?&#60;*...) )
(*naplb:...) ) synonyms
(*non_atomic_positive_lookbehind:...) )
</PRE>
</P>
</pre>
</p>
<br><a name="SEC25" href="#TOC1">SUBSTRING SCAN ASSERTION</a><br>
<P>
<p>
This feature is not Perl-compatible.
<pre>
(*scan_substring:(grouplist)...) scan captured substring
@@ -574,20 +574,20 @@ The comma-separated list may identify groups in any of the following ways:
&#60;name&#62; name
'name' name
</PRE>
</P>
</pre>
</p>
<br><a name="SEC26" href="#TOC1">SCRIPT RUNS</a><br>
<P>
<p>
<pre>
(*script_run:...) ) script run, can be backtracked into
(*sr:...) )
(*atomic_script_run:...) ) atomic script run
(*asr:...) )
</PRE>
</P>
</pre>
</p>
<br><a name="SEC27" href="#TOC1">BACKREFERENCES</a><br>
<P>
<p>
<pre>
\n reference by number (can be ambiguous)
\gn reference by number
@@ -601,10 +601,10 @@ The comma-separated list may identify groups in any of the following ways:
\g{name} reference by name (Perl)
\k{name} reference by name (.NET)
(?P=name) reference by name (Python)
</PRE>
</P>
</pre>
</p>
<br><a name="SEC28" href="#TOC1">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a><br>
<P>
<p>
<pre>
(?R) recurse whole pattern
(?n) call subroutine by absolute number
@@ -620,10 +620,10 @@ The comma-separated list may identify groups in any of the following ways:
\g'+n' call subroutine by relative number (PCRE2 extension)
\g&#60;-n&#62; call subroutine by relative number (PCRE2 extension)
\g'-n' call subroutine by relative number (PCRE2 extension)
</PRE>
</P>
</pre>
</p>
<br><a name="SEC29" href="#TOC1">CONDITIONAL PATTERNS</a><br>
<P>
<p>
<pre>
(?(condition)yes-pattern)
(?(condition)yes-pattern|no-pattern)
@@ -644,9 +644,9 @@ The comma-separated list may identify groups in any of the following ways:
Note the ambiguity of (?(R) and (?(Rn) which might be named reference
conditions or recursion tests. Such a condition is interpreted as a reference
condition if the relevant named group exists.
</P>
</p>
<br><a name="SEC30" href="#TOC1">BACKTRACKING CONTROL</a><br>
<P>
<p>
All backtracking control verbs may be in the form (*VERB:NAME). For (*MARK) the
name is mandatory, for the others it is optional. (*SKIP) changes its behaviour
if :NAME is present. The others just set a name for passing back to the caller,
@@ -671,9 +671,9 @@ pattern is not anchored.
</pre>
The effect of one of these verbs in a group called as a subroutine is confined
to the subroutine call.
</P>
</p>
<br><a name="SEC31" href="#TOC1">CALLOUTS</a><br>
<P>
<p>
<pre>
(?C) callout (assumed number 0)
(?Cn) callout with numerical data n
@@ -682,9 +682,9 @@ to the subroutine call.
The allowed string delimiters are ` ' " ^ % # $ (which are the same for the
start and the end), and the starting delimiter { matched with the ending
delimiter }. To encode the ending delimiter within the string, double it.
</P>
</p>
<br><a name="SEC32" href="#TOC1">REPLACEMENT STRINGS</a><br>
<P>
<p>
If the PCRE2_SUBSTITUTE_LITERAL option is set, a replacement string for
<b>pcre2_substitute()</b> is not interpreted. Otherwise, by default, the only
special character is the dollar character in one of the following forms:
@@ -700,8 +700,8 @@ special character is the dollar character in one of the following forms:
</pre>
For ${n}, n can be a name or a number. If PCRE2_SUBSTITUTE_EXTENDED is set,
there is additional interpretation:
</P>
<P>
</p>
<p>
1. Backslash is an escape character, and the forms described in "ESCAPED
CHARACTERS" above are recognized. Also:
<pre>
@@ -719,8 +719,8 @@ CHARACTERS" above are recognized. Also:
2. The Python form \g&#60;n&#62;, where the angle brackets are part of the syntax and
<i>n</i> is either a group name or a number, is recognized as an alternative way
of inserting the contents of a group, for example \g&#60;3&#62;.
</P>
<P>
</p>
<p>
3. Capture substitution supports the following additional forms:
<pre>
${n:-string} default for unset group
@@ -728,23 +728,23 @@ of inserting the contents of a group, for example \g&#60;3&#62;.
</pre>
The substitution strings themselves are expanded. Backslash can be used to
escape colons and closing curly brackets.
</P>
</p>
<br><a name="SEC33" href="#TOC1">SEE ALSO</a><br>
<P>
<p>
<b>pcre2pattern</b>(3), <b>pcre2api</b>(3), <b>pcre2callout</b>(3),
<b>pcre2matching</b>(3), <b>pcre2</b>(3).
</P>
</p>
<br><a name="SEC34" href="#TOC1">AUTHOR</a><br>
<P>
<p>
Philip Hazel
<br>
Retired from University Computing Service
<br>
Cambridge, England.
<br>
</P>
</p>
<br><a name="SEC35" href="#TOC1">REVISION</a><br>
<P>
<p>
Last updated: 27 November 2024
<br>
Copyright &copy; 1997-2024 University of Cambridge.