javascript - JS中的正则表达式

Question

你能帮我理解以下正则表达式的含义吗:

(?:.*? rv:([\w.]+))?

所以，

(?: //the pattern must be in a string, but doesn't return
. //any Unicode character except newline
* //zero or more times
? //zero or one time (how is *? different from just *)
rv: //just "rv:" apparently
[\w //any digit, an underscore, or any Latin-1 letter character
.] //...or any unicode character (are Latin-1 characters not Unicode?)
..))? //all that zero or one time

它来自“权威指南”，我讨厌那本书。非常感谢一些与正则表达式匹配和不匹配的示例。

Answer 1

正则表达式是:

(?:    # begin non capturing group
.*?    # any character, zero or more times, but peek and stop if the next char is
       # a space (" "); then look for
rv:    # literal "rv:", followed by
(      # begin capturing group
[\w.]  # any word character or a dot (the dot HAS NO special meaning in a character class),
+      # once or more,
)      # end capturing group
)      # end non capturing group
?      # zero or one time

*? 是所谓的惰性量词，它强制正则表达式引擎在吞下一个字符之前先查看下一个字符——它被使用、过度使用和滥用，这是一种情况:由于下一个字符是文字​​空格，因此必须将其替换为 [^ ]*(任何不是空格的内容，零次或多次)，这完全避免了前瞻。

确定性的。对。