The PCRE extension is a core PHP extension, so it is always enabled. By default, this extension is compiled using the bundled PCRE library. Alternatively, an external PCRE library can be used by passing in the --with-pcre-regex=DIR configuration option where DIR is the location of PCRE's include and library files.
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.
Before PHP 5.3.0, this extension could be disabled by passing in the --without-pcre-regex configuration option.
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 It is possible that certain parts of the PHP documentation is outdated, in that it may not cover the newest features that PCRE provides.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:
|PHP Version||Updated PCRE Version||Notes|
|5.5.26 / 5.6.9||8.37|
|5.5.0 / 5.4.14 / 5.3.24||8.32|
|5.4.9 / 5.3.19||8.31|