>> We’d definitely need more opinions, especially from folks like
>> Werner who have worked on the docs/appendices a lot, as well as
>> from users: how do they feel about it? How much do they use which
>> index?
I use Appendix E only.
> While people are thinking, what do you think about the idea that
> contents of indices aren't supposed to overlap? (Maybe flip to the
> back of a few actual books here to check?)
I very much dislike that. We use different fonts (via different
indexing commands) to provide a clear distinction between concepts and
commands, and LilyPond's clean naming schemes for properties, context,
engravers, etc., should additionally help a user to find the stuff he
or she needs.
Looking into one of the most complicated books regarding indices, the
new, third edition of the 'LaTeX companion', I see that it has only a
single index (with both concepts and commands) – this two-volume book
has in total about 1500 pages (not counting the indices), and the
index is about 150 pages.
Werner