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Regex

3.7 Grouping Operators (( ... ) or \( ... \))

A group, also known as a subexpression, consists of an open-group operator, any number of other operators, and a close-group operator. Regex treats this sequence as a unit, just as mathematics and programming languages treat a parenthesized expression as a unit.

Therefore, using groups, you can:

• delimit the argument(s) to an alternation operator (see section 3.5 The Alternation Operator (| or \|)) or a repetition operator (see section 3.4 Repetition Operators).

• keep track of the indices of the substring that matched a given group. See section 7.1.8 Using Registers, for a precise explanation. This lets you:
  • use the back-reference operator (see section 3.8 The Back-reference Operator (\digit)).

  • use registers (see section 7.1.8 Using Registers).

If the syntax bit RE_NO_BK_PARENS is set, then `(' represents the open-group operator and `)' represents the close-group operator; otherwise, `\(' and `\)' do.

If the syntax bit RE_UNMATCHED_RIGHT_PAREN_ORD is set and a close-group operator has no matching open-group operator, then Regex considers it to match `)'.