Others
Anchors
^ | The match must start at the beginning of the string or line. |
$ | The match must occur at the end of the string or before \n at the end of the line or string. |
Backreference Constructs
\number | Backreference. Matches the value of a numbered subexpression. |
\k<name> | Named backreference. Matches the value of a named expression. |
Alternation Constructs
| | Matches any one element separated by the vertical bar (|) character. |
(?(expression)yes|no) | Matches yes if expression matches; otherwise, matches the optional no part. expression is interpreted as a zero-width assertion. |
(?(name)yes|no) | Matches yes if the named capture name has a match; otherwise, matches the optional no. |