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Starting at release 3.3, PCRE has had some support for character strings encoded in the UTF-8 format. For release 4.0 this has been greatly extended to cover most common requirements.
In order process UTF-8 strings, you must build PCRE to include UTF-8 support in the code, and, in addition, you must call pcre_compile() with the PCRE_UTF8 option flag. When you do this, both the pattern and any subject strings that are matched against it are treated as UTF-8 strings instead of just strings of bytes.
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A "word" character is any letter or digit or the underscore character, that is, any character which can be part of a Perl "word". The definition of letters and digits is controlled by PCRE's character tables, and may vary if locale- specific matching is taking place (see "Locale support" in the pcreapi page). For example, in the "fr" (French) locale, some character codes greater than 128 are used for accented letters, and these are matched by \w.
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Named capturing parentheses are still allocated numbers as well as names. The PCRE API provides function calls for extracting the name-to-number translation table from a compiled pattern. For further details see the pcreapi documentation.