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[A-Man]

Ah well, I am pretty sure you've given this more thought, and you've pretty much considered a lot more than what it seems in what you've mentioned. But why limit it to regular expressions? Did you consider a normal string-manipulation approach? That might be simpler to get right than getting regular expressions to work. I happen to have a js snippet which parsed stuff like that flawlessly (as far as I have tested).

Edit: What are some examples that may cause a problem in the layout or become a security exploit? Are you concerned with modifying the core files? (I mean you've only recently updated to the new version)