FYI,
Here is a simple example to find the word "title" *not* inside a tag itself, here is the simplest regex search I could think of off the top of my head. It assumes there is no bare text in the body tag and that the xhtml is well formed.
I tried it and it appears to work. There are probably better more exhaustive regex, that can handle even broken xhtml.
This basically says search for "title" but lookahead to make sure there are no closing tag chars ">" before you find the next opening tag char "<".
There are probably look behind versions that could work with reverse logic. And there are ways to use regex to find a two strings that ignores any intervening tags.
Give it a try. You could add a saved search easily to do that. But again it will not handle find and replacement of text that crosses over elements (over nodes in the tree). That is the hard part unless you have one to one corresponding matching of matching substrings to replacement substrings which in general need not be the case.
And of course if you use < and > inside strings to show a "tag" or code snippet, these would be found by mistake so reviewing each find before the replace would be needed.