good news! created a successful spanning engraver entirely on the scheme end.

[Mike Solomon]

Hey lilyponders,
    I was able to create a spanner that has more or less the same
functionality as TextSpanner entirely out of scheme in a ".ly" file.  I used
the newly-christened ly:announce-end-grob as well as ly:grob-chain-callback
and ly:engraver-property, both of which I've uploaded to Reitveld and are
waiting review.  As soon as they get commented upon and (hopefully) applied
to the source, I will send out a regression test.

~Mike