Piano pedalling

[Chris Jackson]

I'm trying to investigate how to implement the
|___/\_______/\__________|  style of piano sustain pedalling.

Adding a 'edge-width' property to the generic text spanner, to go with
'edge-height' doesn't look too hard.  Then a macro, such as
\sustainBracketStart/Stop/Restart, might be written to start and stop
the text spanner with the required properties set to sensible values.

But what would be the best way of ensuring that successive brackets on
the same staff are automatically typeset at the same y-distance below
the staff, without having to hand-tweak the properties every time the
notes go too low? 

-- 
chris