反向引用构造允许随后在相同的正则表达式中识别先前匹配的子表达式。
下表列出了这些构造−
| Backreference construct | Description | Pattern | Matches |
|---|---|---|---|
| \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" |
