The syntax for patterns used in these functions closely resembles Perl. The expression should be enclosed in the delimiters, a forward slash (/), for example. Any character can be used for delimiter as long as it's not alphanumeric or backslash (\). If the delimiter character has to be used in the expression itself, it needs to be escaped by backslash. Since PHP 4.0.4, you can also use Perl-style (), {}, [], and <> matching delimiters.
The ending delimiter may be followed by various modifiers that affect the matching. See Pattern Modifiers.
PHP also supports regular expressions using a POSIX-extended syntax using the POSIX-extended regex functions..
Regular expression support is provided by the PCRE library package, which is open source software, written by Philip Hazel, and copyright by the University of Cambridge, England. It is available at ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/.
Beginning with PHP 4.2.0 this function are enabled by default. For older versions you have to configure and compile PHP with --with-pcre-regex[=DIR] in order to use these functions. You can disable the pcre functions with --without-pcre-regex.
This extension does not define any configuration directives.
This extension does not define any resource types.
PREG_PATTERN_ORDER PREG_SET_ORDER PREG_SPLIT_NO_EMPTY PREG_SPLIT_DELIM_CAPTURE