OK, i found the new panel it opens and it does Find non-tagged text
My unsolicted comments are that it seems to operate very differently than the 'standard' Find/Replace
I can't do a [Replace] or [Replace all] or [Replace find next]. The triangle icons for Find next and find previous work nicely but only to jump to the next occurance.
It would be my guess that if a user was looking for non-tagged text, a replacement would be common thing to do

I'd be my thought that just using a fourth check box by
[ ] Case Sensitive [ ] Wrap [ ] Dot all [ ] Ignore HTML markup
would be more flexible