> If you use Emacs outline-mode or the GNU Hyperbole package's Koutliner mode, you'll see they both move past invisible *lines* of text all at once.

As far as I see, they still create overlays that span the hidden lines and convey `invisible' property. So I don't really see how anything depends on it being complete lines (in my cases that's also the case) or not...

> Each Emacs buffer contains a buffer-display-table with a display-table slot that handles invisible lines.  See the doc. for buffer-display-table.

I checked this variable and it's also nil in an Outline buffer. Besides, its documentation says it's about characters, so it doesn't seem relevant to me.

Paul