[texhax] architectural documentation for low-level LaTeX functions?

[Niall Mansfield]

I'm writing a document class based on "book.cls" and am having
trouble with sections/subsections -- in particular getting
the right (sub)section numbers in headings and TOCs.

Is there any "architectural" documentation available on 
low-level functions, e.g. how \@startsection, \@ssvsec, \@svsechd,
\@sect, \@ssect, etc. interact?

(The ltsect.dtx file describes the code but doesn't explain
how the various functions interact, or why, or even why you would
want them.)

	Niall Mansfield