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Pattern matching
Grouping

Grouping

Grouping

Sequence

Description

(...)

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.

**Options**
Option	Description
i	Case insensitive.
-i	Case sensitive.
s	Alters the meaning of '.' to match any character whatsoever.
-s	Alters the meaning of '.' to match any character except '\n'.
x	Ignores 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.