Lilypond Architectural Overview Request

[jim.showalter]

I have been reviewing the online manuals and am having trouble finding
documentation that describes the overall architecture of the Lilypond
system.  I am primarily talking about the interaction of .ly and .scm files
(how they are parsed by the C++ code would be welcome too).  When I look at
the Internals Reference, for example, it looks like it would be very useful
for someone who was already familiar with the call sequences and class
structure and the overall operation of lilypond.  But I haven't found
something which explains how everything actually ties together.  For
example, the contents of the types list for an AbsoluteDynamicEvent are
'(general-music event dynamic-event absolute-dynamic-event).  This looks
almost like a class event hierarchy of said event.  But I could not find
what general-music meant (I searched the pdf files) or how each element in
the list relates to each other.  Elsewhere I found the general-music term at
the end of a types list.  I checked the bnf but that just specifies syntax.
Of course this is just one of many mysteries I would like to understand.

Thanks,
Jim