doc: Degraded usefulness of search results

[panicbit]

Compare these search results in 1.22.1 and nightly (ad3543db3 2017-12-08):

No results, even though there are trivial and useful matches.

Irrelevant results. Most relevant results are offscreen, two pages down.

[GuillaumeGomez]

That's problematic, indeed. I'll add another check for "starts_with" or something along the lines.