.	[^\n\r] or [^\n]|\n in s mode
\s	[#x20\t\n\r]
\S	[^\s]
\i	the set of initial name characters, those ·match·ed by Letter | '_' | ':'
\I	[^\i]
\c	the set of name characters, those ·match·ed by NameChar
\C	[^\c]
\d	\p{Nd}
\D	[^\d]
\w	[#x0000-#x10FFFF]-[\p{P}\p{Z}\p{C}] (all characters except the set of "punctuation", "separator" and "other" characters)
\W	[^\w]


s mode - . matches all characters
m mode - ^ and $ match start and end of any line
i mode - case insensitive
x mode - remove whitespace from pattern, apart from