--- /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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