Except two minor remarks, this is great!
Where are those? Since I can't find them, maybe a minor remark of my own :-).
Maybe we should consider what widget in the sidebar gets the focus by default - right now it's the entry (and the tree focus is just one `tab` or `enter` press away) but maybe users who use primarily keyboard are more used to having the tree focused. I don't mind much myself as I just use mouse for the tree.
I'd expected that it required more code to make the filter per document but happy to be proven wrong :D.
Same here and it actually applies to the whole patch. I was thinking about this feature for a long time but thinking it would be annoying to do and then saw the pull request which was pretty trivial and mostly working so I got attracted :-).
Gentle prompt, its a UI change and new functionality so manual change also needed.
Sure, if it's something that's going to be merged, I'll definitely update it.