I have previously asked about the possibility of markers in a MuseScore score - but this has been answered partly at least by the use of Rehearsal Marks. Maybe this is not a perfect or comprehensive solution to some problems, but it is a useful thing to know about.
What would make a marker system even more useful would be the equivalent of a contents list and an index.
Currently I use sections of scores to try out ideas rather than having a new score for each idea. It would be very useful to be able to have a contents list or index of all the ideas in a score. Note that rehearsal marks might not quite do the job, as presumably each rehearsal mark should be unique, whereas it is possible that - just as in a written text - the same idea might occur in more than one location.