Hey Kirby,
That is indeed outlandish and probably a syntax difference with ICU regular expressions.
But as Peter said it's really difficult to help without a real data-sample to test against.
I do this sort of thing all the time, although I use the AppleScript and the Satimage.osax for my find and find/replace actions.
If you're parsing HTML you should also consider talking directly to Safari or Chrome and using Xpath instead of RegEx.
An example can be found here.
-Chris