Введение
  Подсказка
   
    PHP also supports regular expressions using a Perl-compatible syntax
    using the PCRE functions. Those functions
    support non-greedy matching, assertions, conditional subpatterns, and a
    number of other features not supported by the POSIX-extended regular
    expression syntax.
   
   
  Внимание
   
    These regular expression functions are not binary-safe. The PCRE functions are.
   
   
  Замечание: 
   
    As of PHP 5.3.0 this extension is deprecated, calling any function 
    provided by this extension will issue an E_DEPRECATED 
    notice.
   
  
  
   Regular expressions are used for complex string manipulation.
   PHP uses the POSIX extended regular expressions as defined by POSIX
   1003.2. For a full description of POSIX regular expressions see the » regex
   man pages included in the regex directory in the PHP distribution. It's
   in manpage format, so you'll want to do something along the lines of
   man /usr/local/src/regex/regex.7 in order to read it.