> I am working on the model-based selection like lists can do. There is a hook
> for that (#selectMorphByFilter or such).

That's great!  This would allow the user to "navigate" by their
fingers from the home row.

> Command keys will be back soon. Actually, it were never command keys but
> simple key presses such as $i for inspect. I want to change them to CMD+i so
> that both can work at the same time.

Ha!  All these years I was pressing the Command+key unnecessarily.
Good so now I've got the right habits established for this new
feature.  :)

> For the search, I think about considering the current selection and search
> that subtree after typing stuff. Backspace could remove only the filter for
> the selected sub-tree. How does that sound? You could use the feature as a
> whole tree exploration tool.

That sounds very powerful, I love it!  We are dealing with a
hierarchy, so there are a couple of different ways to approach this
isn't there?

For example, another approach I thought about was, it would only
search whatever nodes were actually *visible* (the already-expanded
subtrees), regardless of what level they were at.  This would
eliminate the need for the MaxDepth preference, but the shortcoming is
that the user would have to expand a bunch of nodes in advance just to
"prepare it" for filtering -- so this works against the navigation
use-case.

So, I think your idea provides the best of all worlds:  navigation,
subselection, and filtering.  Well done!

> Depth of 1 is fine for me. I did not collect much experience with this
> feature yet.

Me neither and maybe we'll want to bump it to 2 but I thought it would
be good to start conservative and see how well it works.

You are really rocking, thanks!