Backreference constructs allow a previously matched sub-expression to be identified subsequently in the same regular expression.
The following table lists these constructs −
|\ number||Backreference. Matches the value of a numbered subexpression.||(\w)\1||"ee" in "seek"|
|\k< name >||Named backreference. Matches the value of a named expression.||(?< char>\w)\k< char>||"ee" in "seek"|