All,
In #perl tonight on IRC, someone asked how to match 'Foo::Bar' but not match 'Foo::Bar\s*(' Not having very strong fu, I looked up perlre and found a negative lookahead assertion 
/Foo::Bar(?!\s*\()/

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I was told that it was inadequate because it didn't work in the general case (where Foo::Bar is getting replaced by \w+::\w+). I found that Foo could change to \w+ without a problem but that Bar couldn't. I believe this has to do with the 0-width part about assertions but why, in plain english, doesn't the following work? 
/\w+::\w+(?!\s*\()/

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And - how would I properly answer this question in the future? While I have never tried to claim I had more regex knowledge then I have - I find not knowing the answer to this a bit embarrasing after using the language for 3 years.

Cheers - L~R

Update:Thanks all! I really should spend some time with The Owl and TFM.

In reply to Negative Lookahead Assertion Problem by Limbic~Region

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