... too often, with the triangles, they were made equilateral, so it was never clear from just looking at them whether or not they were collapsed or expanded.
Interesting. Similar to the "confusion" I experience with the single-state downward chevron "V" often found in MC Options submenus. That's what launched me on this quest for an alternative. I think the 3-bar menu symbol resolves it, very contemporary though some may consider it a little heavy-handed for this application. The filled right chevron also works for me, probably because I am so conditioned to expect it to open a menu to the right. At least JRiver makes it relatively easy to try both.
One might expect that the filled downward chevron, usually found in a selected view tab, would be confusing for same reasons as the "V". Except that the dropdown menu appears immediately with a mouseover, and there are no closely adjacent copies of the same static symbol, which together effectively resolve it for me.
Re circles for the top level tree branch expansion - never saw your old posts in this regard, but I agree with you - immediate fast visual information, no thinking about right v.s. down pointers is required! Though like most symbology, it still takes a little learning. And as you might guess by now, I am always on the lookout for minimalist solutions! However, enhancement with a gentle 3-state response would be nice to try here. I hope it could be made backward compatible with existing 2-state treatments as long as the
NumberImages parameter agrees with the artwork.