I’ve added a couple of new outline functions beneath the View menu. These will work on both the Tags tab and the (optional) Outline tab. One will collapse everything, leaving only the topmost items visible. The other will expand everything. Both have keyboard shortcuts (mirroring similar commands in OmniOutliner).
I’ll be interested in hearing how these work for people!
This beta version is no longer available. Look for a later beta release or the most recent Mac App Store release.