It 100% depends on what your requirements are.I use TextWrangler on MacOS, and I find it's not even worth the effort of limiting searches narrower than the whole game folder, with 11 text filetypes. It only takes about 6 seconds to search the entire CK2 folder for a simple keyword, a bit longer if I do interesting grep/regex patterns.
It's usually far more important to figure out *what* to search. In this case, based on OP's question, I searched for the word 'drill'. The bloodline entry quoted above was the 2nd result, but had it not been so obvious, a quick scan down the results would have found it. Simpler than having to repeat the search should you guess the sub-folder wrong.
I'm not convinced indexing is that helpful. As noted above, a simple search of the whole CK2 folder in 11 text filetypes takes about 6 seconds. Sometimes, the important info is *in* the gui, gsx, or loc files. The only things I make an effort to avoid is the binary files (executable, pics, sounds, etc.)
And I don't have to worry about re-indexing after each patch.
As a professional developer; if I had to wait 6 seconds(or even half of that) for the result, I would go looking for a new tool. In reality, I also think the time would be at least double since I also search the source code. I also have additional requirements on my tool as I want it to work well with all the other ones I use and support more advanced features.
I was just giving advice on a tool I think is really good (It actually helps quite a bit with the "what to search" problem as well), and everyone is free to use whatever they wish