Delimiters
Backslash
PCRE regex syntax
PHP Manual

## Meta-characters

The power of regular expressions comes from the ability to include alternatives and repetitions in the pattern. These are encoded in the pattern by the use of meta-characters, which do not stand for themselves but instead are interpreted in some special way.

There are two different sets of meta-characters: those that are recognized anywhere in the pattern except within square brackets, and those that are recognized in square brackets. Outside square brackets, the meta-characters are as follows:

\
  general escape character with several uses
^
  assert start of subject (or line, in multiline mode)
$
  assert end of subject (or line, in multiline mode)
.
  match any character except newline (by default)
[
  start character class definition
]
  end character class definition
|
  start of alternative branch
(
  start subpattern
)
  end subpattern
?
  extends the meaning of (, also 0 or 1 quantifier, also makes greedy quantifiers lazy (see repetition)
*
  0 or more quantifier
+
  1 or more quantifier
{
  start min/max quantifier
}
  end min/max quantifier

Part of a pattern that is in square brackets is called a "character class". In a character class the only meta-characters are:

\
  general escape character
^
  negate the class, but only if the first character
-
  indicates character range
]
  terminates the character class

The following sections describe the use of each of the meta-characters.

Delimiters
Backslash
PCRE regex syntax
PHP Manual