Architecture for Fret Diagrams

[Carl Sorensen]

I've been studying and thinking about architectures for Fret Diagrams in
lilypond.

It seems to me that there should be a FretDiagrams context which would
process exactly the same music expression as the ChordNames context. 
Then, a lead sheet with fret diagrams could look like:

\score {
       <<
         \new ChordNames \chords { chords }
         \new FretDiagrams \chords { chords }
         \notes the melody
         \lyricsto "" \new Lyrics \lyrics { the text }
       >>
     }


As far as the Fret_diagrams_engraver goes, I'm thinking that it could
work as follows:  If there are no string events, then it could just do
an alist lookup for the fret diagram, based on the chord name, which is
available using the code from the Chord_name_engraver.  If there are
string events, then it could create the fret diagram using the string
(and possibly finger) events.

First, does this architecture seem reasonable?

Second, where do I look to find out how a context is created?

Third, can I just call make-item, setting the "text" property to be a
fret-diagram markup, much like the Chord_name_engraver does now?  If
not, how do I use make-item, or where can I find out more about how to
use make-item?

Thanks,

Carl Sorensen