What does (?: do in a regular expression

Question

I have come across a regular expression that I don\'t fully understand - can somebody help me in deciphering it:

^home(?:\\/|\\/index\\.asp)?(?:\\?.+)?$
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Answer 1

It's a non-capture group, which essentially is the same as using (...), but the content isn't retained (not available as a back reference).

If you're doing something like this: (abc)(?:123)(def) You'll get abc in $1 and def in $2, but 123 will only be matched.