[Tracker] Documentation? Query options?

[Johann Petrak <johann petrak chello at>]

I find the documentation of tracker rather lacking: there is not even a
help button in the search GUI anywhere.

I especially miss information on how to do more than just the most
primitive queries in the GUI: how can one limit the query to just
files of a specific type, e.g. PDF, or just HTML or to other
metadata fields? Is there a way to only search within a certain
directory? Is there a way to exclude search terms, do phrase
search or near searches? Boolean search?
What options does the user have?