(...)Group a regular expression to override default operator precedence.
(?r-s:pattern) Apply option r and omit option s while interpreting pattern. Options may be zero or more of the characters i, s, or x.
iCase insensitive.
-iCase sensitive.
sAlters the meaning of '.' to match any character whatsoever.
-s"lters the meaning of '.' to match any character except '\n'.
xIgnores comments and whitespace in patterns. Whitespace is ignored unless it is backslash-escaped, contained within ""s, or appears inside a character range.
These options can be applied globally at the rules level by passing a combination of the bit flags to the lexer.
(?# comment )Omit everything within (). The first ) character encountered ends the pattern. It is not possible for the comment to contain a ) character. The comment may span lines.