is "pure positioning" done per score or per bookpart?

[Jeff Olson]

Jean,

I'm studying your "Overview of LilyPond’s inner workings" 
(https://extending-lilypond.readthedocs.io/en/latest/intro.html#overview-of-lilypond-s-inner-workings-and-how-you-might-hook-in-them) 
and trying to correlate the processing steps you describe with the INFO 
level output that I can see in the log.

Knowing my piece, I can discern in the log what's done e.g. for every 
score from things that are done for each bookpart:

   per compile:   "Parsing..."
   per score:     "Interpreting music...[8][16][24][32][40][48]"
   per score:     "Preprocessing graphical objects..."
   per bookpart:  "Finding the ideal number of pages..."
   per bookpart:  "Fitting music on 39 or 40 pages..."
   per bookpart:  "Drawing systems..."
   per compile:   "Converting to <myfile>.pdf"

But what is not self-evident is whether the stage you label as "Pure 
Positioning" is done per score in "Preprocessing graphical objects..." 
or per bookpart in "Finding the ideal number of pages...".

Since pure positioning is done a priori, before breaks are decided, it 
could be per score.  But the word "ideal" in the log might alternatively 
match with "pure".

This off-by-one ambiguity cascades through the subsequent stages and 
their correlation with log messages, but surprisingly both possibilities 
arguably line up with the log.

I guess I could equivalently ask whether the stage "Writing Output" is 
done for each bookpart or once for the whole compilation.

If you're still taking suggestions re extending-lilypond.readthedocs.io, 
it might help others if each of the processing stages listed in the 
Overview explicitly said how they appear in the log, since those phrases 
are often familiar even to Frescobaldi users.

Thanks,
Jeff