Re: how offsets and alignment works: an explanation

[Noeck]

> here's an explanation of what's happening when we're using XY-offset,
> self-alignment etc.  I hope that it'll help users get a better
> understanding of LilyPond internals; i also think it would be a good
> material for documentation, 

Hi Janek,

I loved to read this long mail. I would like to see the first half of it
in the notation reference. Things like the reference point, X- and
Y-offsets and X- and Y-extents should be explained, because users need
this knowledge for any shifts.

As far as I can see this is not explained in the NR, but this section
the user is expected to know it already:
http://lilypond.org/doc/v2.16/Documentation/notation/aligning-objects

I would be interested in the reference point for various additional
objects, e.g. dynamics, as an extension to your "repoint example.png". I
did not know for example, that it is on the left for note heads.

Scheme functions like ly:self-alignment-interface::x-aligned-on-self, I
would consider for the extension manual.

Thanks a lot for this!
Joram