Symbols are a new thing that have subordering and duration like text events, for example performance directions, tempo indications, and other such that are no-ops from a sequencer perspective, but will display suitable glyphs on the staff instead of arbitrary or canned texts. The first three of these are the segno, coda, and breath mark, which aim to be a 1:1 replacement for the LilyPond directive Text tool based hacks that have been working and exportable for some time.
I expect that's about as far as I will take the new concept for Thorn's release, lest I get too sidetracked with fun and entertaining projects instead of the backbreaking but mandatory work of repairing critical infrastructure and readying everything for release.
So these are random thoughts I have looking through note fonts for glyphs I might want to do as Symbols one day:
the “repeat last measure” thing '/. (and what are / and '. for anyway? I'm not sure, but they may be worth including)
* arpeggio wave thingies
* replace the whole horrible NextBarIsAlt1 garbage with what? And draw it properly. (This one seems pretty hard, because this was implemented as a flag to exist in the bar before it would take effect for processing reasons. In the near term, it might be all we could realistically manage would be a pretty indicator instead of the lame green text thing. That might be workable if it spanned a barline, and looked like Alt 1 —→ |1.———- as one big wide thing where the active bit would be in the right bar, and the inactive visual bit would or could at least sit in the correct place to make some musical sense, instead of leaving everything to the user's imagination as is currently the case with this hideous mechanism I've never properly explained to anyone, which is almost unusable, but just barely not.)
* some suitable hackery for barlines that might needs out of practicality resemble the above. Put the active bit just ahead of the affected barline, and then show what it's going to do visually. Or maybe just make barlines real entities in the process of sorting out the whole “raising the bar” discussion that never was, which is apparently all on you.
These might ought to be indications instead, actually:
* glisando lines