Trying to get a hang of what to use when...

[David Kastrup]

Ok, I am trying to figure out for what kind of task one would use what
kind of Lilypond construct.  So I try echoing my current understanding
and want you to holler when I am wrong.

We have music functions.  Music functions can be used for doing music
in, music out.  Now music can be complex, containing chords, material of
several durations, markups, context switches (?), parallel music.  The
main nuisance with music functions is that you need to deal with
everything.  Also there are things like bar checks which don't make
sense while interpreting a music expression, but need to be passed down
to some context where some engraver will pick them up and complain or
not.

If we need to process all of this in a sort of sequential manner, like
if we are trying to construct a combined part, or trying to play
something, or trying to engrave a staff or so, we need a context, right?
A context consists of a number of engravers who are more or less able to
selectively grab material passing through the context,
time-sequentially.  A context needs to deal with everything as well, by
using suitable engravers.

If we just want to pick out what we are interested in,
time-sequentially/sorted and leave the rest alone, like lyrics and
stuff, we use an engraver.  How do we signal that we have picked
something and that no other engraver need bother with it?

An engraver really is the same thing as a performer and a translator.
Hopefully.

Corrections?

Thanks.

-- 
David Kastrup