\
\c
x{3,1}
x{99999}
[abc
[z-a]
*
(?h)
[:alpha:]
(abc
abc\3
(?#abc
)
(?<x)y
(?<=a*)y
(?()abc)
(xy)(?(1)abc|def|ghi)
(?(*))
(?R*)
[[:fnord:]]
\\x{123456}
(?(0))
(?<=\C)
\l
(?C256)
(?C1
(?R)
(?P*)
(?P<*>x)
(?P<aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa>)
\777
^ignoreme$