I couldn't find any documentation on how to use tags, etc. for searching (the same was true for nepomuk), which limits is usefulness. Reproducible: Always
Status Update - We've added a user visible query language for 5.1. It's only visible via kioslaves for 5.1, but you will be able to perform decently complex queries. Eg - baloosearch://?query=tag:A OR tagB baloosearch://?query=artist:Coldplay I'll close this bug when there is some proper documentation on the userbase.
Still no documentation on Baloo kioslaves.
Still valid
This page has better documentation for Nepomuk which Baloo inherits design from: https://techbase.kde.org/Projects/Nepomuk/QueryingMethods
There is a discussion here which might be worth mining... https://old.reddit.com/r/kde/comments/pmcshj/tip_baloosearch_kioslave/ Thanks are due to AiwendilH