+++ /dev/null
-<html>
-<head>
-<title>pcre specification</title>
-</head>
-<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
-<h1>pcre man page</h1>
-<p>
-Return to the <a href="index.html">PCRE index page</a>.
-</p>
-<p>
-This page is part of the PCRE HTML documentation. It was generated automatically
-from the original man page. If there is any nonsense in it, please consult the
-man page, in case the conversion went wrong.
-<br>
-<ul>
-<li><a name="TOC1" href="#SEC1">INTRODUCTION</a>
-<li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>
-<li><a name="TOC3" href="#SEC3">LIMITATIONS</a>
-<li><a name="TOC4" href="#SEC4">UTF-8 AND UNICODE PROPERTY SUPPORT</a>
-<li><a name="TOC5" href="#SEC5">AUTHOR</a>
-<li><a name="TOC6" href="#SEC6">REVISION</a>
-</ul>
-<br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
-<P>
-The PCRE library is a set of functions that implement regular expression
-pattern matching using the same syntax and semantics as Perl, with just a few
-differences. Some features that appeared in Python and PCRE before they
-appeared in Perl are also available using the Python syntax, there is some
-support for one or two .NET and Oniguruma syntax items, and there is an option
-for requesting some minor changes that give better JavaScript compatibility.
-</P>
-<P>
-The current implementation of PCRE corresponds approximately with Perl 5.10,
-including support for UTF-8 encoded strings and Unicode general category
-properties. However, UTF-8 and Unicode support has to be explicitly enabled; it
-is not the default. The Unicode tables correspond to Unicode release 5.1.
-</P>
-<P>
-In addition to the Perl-compatible matching function, PCRE contains an
-alternative function that matches the same compiled patterns in a different
-way. In certain circumstances, the alternative function has some advantages.
-For a discussion of the two matching algorithms, see the
-<a href="pcrematching.html"><b>pcrematching</b></a>
-page.
-</P>
-<P>
-PCRE is written in C and released as a C library. A number of people have
-written wrappers and interfaces of various kinds. In particular, Google Inc.
-have provided a comprehensive C++ wrapper. This is now included as part of the
-PCRE distribution. The
-<a href="pcrecpp.html"><b>pcrecpp</b></a>
-page has details of this interface. Other people's contributions can be found
-in the <i>Contrib</i> directory at the primary FTP site, which is:
-<a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</a>
-</P>
-<P>
-Details of exactly which Perl regular expression features are and are not
-supported by PCRE are given in separate documents. See the
-<a href="pcrepattern.html"><b>pcrepattern</b></a>
-and
-<a href="pcrecompat.html"><b>pcrecompat</b></a>
-pages. There is a syntax summary in the
-<a href="pcresyntax.html"><b>pcresyntax</b></a>
-page.
-</P>
-<P>
-Some features of PCRE can be included, excluded, or changed when the library is
-built. The
-<a href="pcre_config.html"><b>pcre_config()</b></a>
-function makes it possible for a client to discover which features are
-available. The features themselves are described in the
-<a href="pcrebuild.html"><b>pcrebuild</b></a>
-page. Documentation about building PCRE for various operating systems can be
-found in the <b>README</b> and <b>NON-UNIX-USE</b> files in the source
-distribution.
-</P>
-<P>
-The library contains a number of undocumented internal functions and data
-tables that are used by more than one of the exported external functions, but
-which are not intended for use by external callers. Their names all begin with
-"_pcre_", which hopefully will not provoke any name clashes. In some
-environments, it is possible to control which external symbols are exported
-when a shared library is built, and in these cases the undocumented symbols are
-not exported.
-</P>
-<br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
-<P>
-The user documentation for PCRE comprises a number of different sections. In
-the "man" format, each of these is a separate "man page". In the HTML format,
-each is a separate page, linked from the index page. In the plain text format,
-all the sections, except the <b>pcredemo</b> section, are concatenated, for ease
-of searching. The sections are as follows:
-<pre>
- pcre this document
- pcre-config show PCRE installation configuration information
- pcreapi details of PCRE's native C API
- pcrebuild options for building PCRE
- pcrecallout details of the callout feature
- pcrecompat discussion of Perl compatibility
- pcrecpp details of the C++ wrapper
- pcredemo a demonstration C program that uses PCRE
- pcregrep description of the <b>pcregrep</b> command
- pcrematching discussion of the two matching algorithms
- pcrepartial details of the partial matching facility
- pcrepattern syntax and semantics of supported regular expressions
- pcreperform discussion of performance issues
- pcreposix the POSIX-compatible C API
- pcreprecompile details of saving and re-using precompiled patterns
- pcresample discussion of the pcredemo program
- pcrestack discussion of stack usage
- pcresyntax quick syntax reference
- pcretest description of the <b>pcretest</b> testing command
-</pre>
-In addition, in the "man" and HTML formats, there is a short page for each
-C library function, listing its arguments and results.
-</P>
-<br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
-<P>
-There are some size limitations in PCRE but it is hoped that they will never in
-practice be relevant.
-</P>
-<P>
-The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is
-compiled with the default internal linkage size of 2. If you want to process
-regular expressions that are truly enormous, you can compile PCRE with an
-internal linkage size of 3 or 4 (see the <b>README</b> file in the source
-distribution and the
-<a href="pcrebuild.html"><b>pcrebuild</b></a>
-documentation for details). In these cases the limit is substantially larger.
-However, the speed of execution is slower.
-</P>
-<P>
-All values in repeating quantifiers must be less than 65536.
-</P>
-<P>
-There is no limit to the number of parenthesized subpatterns, but there can be
-no more than 65535 capturing subpatterns.
-</P>
-<P>
-The maximum length of name for a named subpattern is 32 characters, and the
-maximum number of named subpatterns is 10000.
-</P>
-<P>
-The maximum length of a subject string is the largest positive number that an
-integer variable can hold. However, when using the traditional matching
-function, PCRE uses recursion to handle subpatterns and indefinite repetition.
-This means that the available stack space may limit the size of a subject
-string that can be processed by certain patterns. For a discussion of stack
-issues, see the
-<a href="pcrestack.html"><b>pcrestack</b></a>
-documentation.
-<a name="utf8support"></a></P>
-<br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>
-<P>
-From release 3.3, PCRE has had some support for character strings encoded in
-the UTF-8 format. For release 4.0 this was greatly extended to cover most
-common requirements, and in release 5.0 additional support for Unicode general
-category properties was added.
-</P>
-<P>
-In order process UTF-8 strings, you must build PCRE to include UTF-8 support in
-the code, and, in addition, you must call
-<a href="pcre_compile.html"><b>pcre_compile()</b></a>
-with the PCRE_UTF8 option flag, or the pattern must start with the sequence
-(*UTF8). When either of these is the case, both the pattern and any subject
-strings that are matched against it are treated as UTF-8 strings instead of
-strings of 1-byte characters.
-</P>
-<P>
-If you compile PCRE with UTF-8 support, but do not use it at run time, the
-library will be a bit bigger, but the additional run time overhead is limited
-to testing the PCRE_UTF8 flag occasionally, so should not be very big.
-</P>
-<P>
-If PCRE is built with Unicode character property support (which implies UTF-8
-support), the escape sequences \p{..}, \P{..}, and \X are supported.
-The available properties that can be tested are limited to the general
-category properties such as Lu for an upper case letter or Nd for a decimal
-number, the Unicode script names such as Arabic or Han, and the derived
-properties Any and L&. A full list is given in the
-<a href="pcrepattern.html"><b>pcrepattern</b></a>
-documentation. Only the short names for properties are supported. For example,
-\p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
-Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
-compatibility with Perl 5.6. PCRE does not support this.
-<a name="utf8strings"></a></P>
-<br><b>
-Validity of UTF-8 strings
-</b><br>
-<P>
-When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
-are (by default) checked for validity on entry to the relevant functions. From
-release 7.3 of PCRE, the check is according the rules of RFC 3629, which are
-themselves derived from the Unicode specification. Earlier releases of PCRE
-followed the rules of RFC 2279, which allows the full range of 31-bit values (0
-to 0x7FFFFFFF). The current check allows only values in the range U+0 to
-U+10FFFF, excluding U+D800 to U+DFFF.
-</P>
-<P>
-The excluded code points are the "Low Surrogate Area" of Unicode, of which the
-Unicode Standard says this: "The Low Surrogate Area does not contain any
-character assignments, consequently no character code charts or namelists are
-provided for this area. Surrogates are reserved for use with UTF-16 and then
-must be used in pairs." The code points that are encoded by UTF-16 pairs are
-available as independent code points in the UTF-8 encoding. (In other words,
-the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up
-UTF-8.)
-</P>
-<P>
-If an invalid UTF-8 string is passed to PCRE, an error return
-(PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that
-your strings are valid, and therefore want to skip these checks in order to
-improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or
-at run time, PCRE assumes that the pattern or subject it is given
-(respectively) contains only valid UTF-8 codes. In this case, it does not
-diagnose an invalid UTF-8 string.
-</P>
-<P>
-If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
-happens depends on why the string is invalid. If the string conforms to the
-"old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
-in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity
-test, PCRE (when in UTF-8 mode) handles strings according to the more liberal
-rules of RFC 2279. However, if the string does not even conform to RFC 2279,
-the result is undefined. Your program may crash.
-</P>
-<P>
-If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
-encoded in a UTF-8-like manner as per the old RFC, you can set
-PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
-situation, you will have to apply your own validity check.
-</P>
-<br><b>
-General comments about UTF-8 mode
-</b><br>
-<P>
-1. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte
-UTF-8 character if the value is greater than 127.
-</P>
-<P>
-2. Octal numbers up to \777 are recognized, and match two-byte UTF-8
-characters for values greater than \177.
-</P>
-<P>
-3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
-bytes, for example: \x{100}{3}.
-</P>
-<P>
-4. The dot metacharacter matches one UTF-8 character instead of a single byte.
-</P>
-<P>
-5. The escape sequence \C can be used to match a single byte in UTF-8 mode,
-but its use can lead to some strange effects. This facility is not available in
-the alternative matching function, <b>pcre_dfa_exec()</b>.
-</P>
-<P>
-6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
-test characters of any code value, but the characters that PCRE recognizes as
-digits, spaces, or word characters remain the same set as before, all with
-values less than 256. This remains true even when PCRE includes Unicode
-property support, because to do otherwise would slow down PCRE in many common
-cases. If you really want to test for a wider sense of, say, "digit", you
-must use Unicode property tests such as \p{Nd}. Note that this also applies to
-\b, because it is defined in terms of \w and \W.
-</P>
-<P>
-7. Similarly, characters that match the POSIX named character classes are all
-low-valued characters.
-</P>
-<P>
-8. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
-(\h, \H, \v, and \V) do match all the appropriate Unicode characters.
-</P>
-<P>
-9. Case-insensitive matching applies only to characters whose values are less
-than 128, unless PCRE is built with Unicode property support. Even when Unicode
-property support is available, PCRE still uses its own character tables when
-checking the case of low-valued characters, so as not to degrade performance.
-The Unicode property information is used only for characters with higher
-values. Even when Unicode property support is available, PCRE supports
-case-insensitive matching only when there is a one-to-one mapping between a
-letter's cases. There are a small number of many-to-one mappings in Unicode;
-these are not supported by PCRE.
-</P>
-<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
-<P>
-Philip Hazel
-<br>
-University Computing Service
-<br>
-Cambridge CB2 3QH, England.
-<br>
-</P>
-<P>
-Putting an actual email address here seems to have been a spam magnet, so I've
-taken it away. If you want to email me, use my two initials, followed by the
-two digits 10, at the domain cam.ac.uk.
-</P>
-<br><a name="SEC6" href="#TOC1">REVISION</a><br>
-<P>
-Last updated: 28 September 2009
-<br>
-Copyright © 1997-2009 University of Cambridge.
-<br>
-<p>
-Return to the <a href="index.html">PCRE index page</a>.
-</p>
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