主要使用的有下面三種：

1.  (...)

Grouping. Group items into a single unit that can be used with *, +, ?, |, and so on. Also remember the characters that match this group for use with later references.

2. (?:...)

Grouping only. Group items into a single unit, but do not remember the characters that match this group.

3.

(?=p)  A positive lookahead assertion. 或

(?!p)  A negative lookahead assertion.

       eg: (\/)匹配url(skins/default/images/index/default.png)

           (\/)default\1匹配url(skins/default/images/index/default.png)

第二種，用于分組，不記錄匹配該分組的字符串

       eg: (?:\/)default匹配url(skins/default/images/index/default.png)

第一、二兩種方式匹配的結(jié)果里都包含有該分組匹配到的結(jié)果，在例子中是"/default"中的"/"

第三種，只用于確定位置，最終結(jié)果里并不包含該括號匹配到的結(jié)果

       eg:  (?!\/)default匹配url(skins/default/images/index/default.png)

       eg:  default(?=\/)匹配url(skins/default/images/index/default.png)

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