Backslash
Circumflex and dollar
PCRE regex syntax
PHP Manual

## Unicode character properties

Since PHP 4.4.0 and 5.1.0, three additional escape sequences to match generic character types are available when UTF-8 mode is selected. They are:

\p{xx}
  a character with the xx property
\P{xx}
  a character without the xx property
\X
  an extended Unicode sequence

The property names represented by xx above are limited to the Unicode general category properties. Each character has exactly one such property, specified by a two-letter abbreviation. For compatibility with Perl, negation can be specified by including a circumflex between the opening brace and the property name. For example, \p{^Lu} is the same as \P{Lu}.

If only one letter is specified with \p or \P, it includes all the properties that start with that letter. In this case, in the absence of negation, the curly brackets in the escape sequence are optional; these two examples have the same effect:

          \p{L}
          \pL

Supported property codes
C | Other
Cc | Control
Cf | Format
Cn | Unassigned
Co | Private use
Cs | Surrogate
L | Letter
Ll | Lower case letter
Lm | Modifier letter
Lo | Other letter
Lt | Title case letter
Lu | Upper case letter
M | Mark
Mc | Spacing mark
Me | Enclosing mark
Mn | Non-spacing mark
N | Number
Nd | Decimal number
Nl | Letter number
No | Other number
P | Punctuation
Pc | Connector punctuation
Pd | Dash punctuation
Pe | Close punctuation
Pf | Final punctuation
Pi | Initial punctuation
Po | Other punctuation
Ps | Open punctuation
S | Symbol
Sc | Currency symbol
Sk | Modifier symbol
Sm | Mathematical symbol
So | Other symbol
Z | Separator
Zl | Line separator
Zp | Paragraph separator
Zs | Space separator

Extended properties such as "Greek" or "InMusicalSymbols" are not supported by PCRE.

Specifying case-insensitive (caseless) matching does not affect these escape sequences. For example, \p{Lu} always matches only upper case letters.

The \X escape matches any number of Unicode characters that form an extended Unicode sequence. \X is equivalent to (?>\PM\pM*).

That is, it matches a character without the "mark" property, followed by zero or more characters with the "mark" property, and treats the sequence as an atomic group (see below). Characters with the "mark" property are typically accents that affect the preceding character.

Matching characters by Unicode property is not fast, because PCRE has to search a structure that contains data for over fifteen thousand characters. That is why the traditional escape sequences such as \d and \w do not use Unicode properties in PCRE.

Backslash
Circumflex and dollar
PCRE regex syntax
PHP Manual