Mats Bengtsson wrote Tuesday, November 10, 2009 5:40 PM
I answer this email for the record.
It seems that there's an attempt to explain this better in the
2.13 manual than in the 2.12 manual, see
http://lilypond.org/doc/v2.13/Documentation/notation/Context-layout-order#Context-layout-order
and
http://lilypond.org/doc/v2.13/Documentation/notation/Aligning-contexts#Aligning-contexts,
but it still doesn't really answer your question.
There's a little more in
http://lilypond.org/doc/v2.13/Documentation/notation/Context-layout-order#Context-layout-order
but even this is not quite complete.
Trevor