Beginning with PHP 4.2.0 these functions are enabled by default. You can disable the pcre functions with --without-pcre-regex . Use --with-pcre-regex=DIR to specify DIR where PCRE's include and library files are located, if not using bundled library. For older versions you have to configure and compile PHP with --with-pcre-regex[=DIR] in order to use these functions.
The Windows version of PHP has built-in support for this extension. You do not need to load any additional extensions in order to use these functions.
As of PHP 5.3.0 this extension cannot be disabled and is therefore always present.
It is still possible to build against an external PCRE library by using --with-pcre-regex=DIR
PCRE is an active project and as it changes so does the PHP functionality that relies upon it. It is possible that certain parts of the PHP documentation is outdated, in that it may not cover the newest features that PCRE provides. For a list of changes, see the » PCRE library changelog and also the following bundled PCRE history:
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