I had a journal request that your final PDF should not contain Type 1 fonts and in my case the culprit were matplotlib figures. I found that with this setting in ~/.config/matplotlib/matplotlibrc
you can make matplotlib avoid Type 1 fonts:

ps.useafm : True
pdf.use14corefonts : True
text.usetex : True

Maybe you consider this useful and can add it here somewhere.

bracketSpan@func documentation:

https://music-encoding.org/guidelines/v4/elements/bracketspan.html

func(required)Describes the function of the bracketed event sequence. Allowed values are: "coloration" (Represents coloration in the mensural notation source material.), "cross-rhythm" (Marks a sequence which does not match the current meter.), "ligature" (Represents a ligature in the mensu

We should rethink the description of what a staff may be, e.g. a staff could be a single line instead of a group, the lines don't have to be equidistant, the lines don't have to be horizontal etc.
The current situation is not satisfactory.

A group of equidistant horizontal lines on which notes are placed in order to represent pitch or a grouping element for individual 'strands' of notes,