是否可以使用另一个正则表达式检测有效的正则表达式？如果是这样，请提供示例代码如下。
@H_403_5@/
^ # start of string
( # first group start
(?:
(?:[^?+*{}()[\]\\|]+ # literals and ^,$
| \\. # escaped characters
| \[ (?: \^?\\. | \^[^\\] | [^\\^] ) # character classes
(?: [^\]\\]+ | \\. )* \]
| \( (?:\?[:=!]|\?<[=!]|\?>)? (?1)?? \) # parenthesis,with recursive content
| \(\? (?:R|[+-]?\d+) \) # recursive matching
)
(?: (?:[?+*]|\{\d+(?:,\d*)?\}) [?+]? )? # quantifiers
| \| # alternative
)* # repeat content
) # end first group
$ # end of string
/
这是一个递归正则表达式，并且不受许多正则表达式引擎支持。基于PCRE的应该支持它。
没有空格和注释：
@H_403_5@/^((?:(?:[^?+*{}()[\]\\|]+|\\.|\[(?:\^?\\.|\^[^\\]|[^\\^])(?:[^\]\\]+|\\.)*\]|\((?:\?[:=!]|\?<[=!]|\?>)?(?1)??\)|\(\?(?:R|[+-]?\d+)\))(?:(?:[?+*]|\{\d+(?:,\d*)?\})[?+]?)?|\|)*)$/.NET不直接支持递归。 ((？1)和(？R)构造)。递归必须转换为计数平衡组：
@H_403_5@^ # start of string (?: (?: [^?+*{}()[\]\\|]+ # literals and ^,$ | \\. # escaped characters | \[ (?: \^?\\. | \^[^\\] | [^\\^] ) # character classes (?: [^\]\\]+ | \\. )* \] | \( (?:\?[:=!] | \?<[=!] | \?> | \?<[^\W\d]\w*> | \?'[^\W\d]\w*' )? # opening of group (?<N>) # increment counter | \) # closing of group (?<-N>) # decrement counter ) (?: (?:[?+*]|\{\d+(?:,\d*)?\}) [?+]? )? # quantifiers | \| # alternative )* # repeat content $ # end of string (?(N)(?!)) # fail if counter is non-zero.压缩：
@H_403_5@^(?:(?:[^?+*{}()[\]\\|]+|\\.|\[(?:\^?\\.|\^[^\\]|[^\\^])(?:[^\]\\]+|\\.)*\]|\((?:\?[:=!]|\?<[=!]|\?>|\?<[^\W\d]\w*>|\?'[^\W\d]\w*')?(?<N>)|\)(?<-N>))(?:(?:[?+*]|\{\d+(?:,\d*)?\})[?+]?)?|\|)*$(?(N)(?!))