Description:
------------
---
From manual page: http://www.php.net/regexp.reference.escape
---
There are currently five valid PCRE escape sequences not documented on this page: \C, \R, \X, \g & \k. Some of these are documented on other pages.

\g & \k - regexp.reference.back-references
\C - regexp.reference.dot
\R matches line break characters or combinations (see http://nikic.github.com/2011/12/10/PCRE-and-newlines.html)
\X matches Unicode graphemes (see http://www.regular-expressions.info/unicode.html)

Also, the description for \G is misleading. \G can also match in preg_match_all or preg_replace at the point where the previous match stopped (see example script).

Test script:
---------------
preg_match_all('/\b([^\Wv]+)\s+/X', "In the beginning the universe was created", $matches, PREG_PATTERN_ORDER, 1); // Matches four words not containing 'v', then followed by a space
var_export($matches[1]);
print("\n");
preg_match_all('/\G\b([^\Wv]+)\s+/X', "In the beginning the universe was created", $matches, PREG_PATTERN_ORDER, 1); // No matches
var_export($matches[1]);
print("\n");
preg_match_all('/\G\b([^\Wv]+)\s+/X', "In the beginning the universe was created", $matches, PREG_PATTERN_ORDER, 3); // Able to match \b at offset 3, then two others. No word can have 'v' in it. \G prevents skipping to next word
var_export($matches[1]);


Actual result:
--------------
array (
  0 => 'the',
  1 => 'beginning',
  2 => 'the',
  3 => 'was',
)
array (
)
array (
  0 => 'the',
  1 => 'beginning',
  2 => 'the',
)