Hello, (Separately reply follows to some of the specific things that were written.)
In case there is interest, what I did now was tweaking the Current_chord_text_engraver from scheme_engravers.scm. It simply takes the first pitch specified in a chord as the root, takes the first one with property "bass" as the bass, and it additionally listens to text-script-events from which it takes the first specified one as the suffix. I use that in a custom context called "HarmonicBackground" for lack of something better, same as ChordNames but with this engraver instead of the original one. For the input I just use relative mode. An example of how I specify the chord symbols now: chords = \relative { <f \over ees>^"7" des^"lyd" } \new HarmonicBackground { \chords} Code can be found here: https://gitlab.com/kbvw/lilypond-tweaks/-/blob/master/harmonic-background.ly It's probably not foolproof; I'm a novice with both LilyPond and Scheme. Currently the text-script is hard-coded to go in the superscript of the chord, before the slash separator. Perhaps it would be nicer to look if the text-script is entered with ^ or _, and even nicer would be to use shorthands in an input mode such as the chord mode, but I didn't look at any of the input/parser code yet. For myself that suffices for now; it looks good to me on the page and it's easy/flexible to enter. If anyone more knowledgeable thinks it's worth continuing with, I'd be happy to discuss/help! (I can see several advantages and disadvantages.) All the best, and thanks for the help, Koen