Function for overriding broken spanners

Function for overriding broken spanners

The music function \alterBroken is intended to facilitate overrides
applied independently to the pieces of broken spanners--one of the
perennial difficulties faced by users of LilyPond (addressed in
Extending 2.6:"Difficult Tweaks").  The function aims at generalization
by allowing the user to specify the name of the spanner and the property
to be overridden.

The function will override unbroken spanners, but it will ignore
non-spanners with a warning.

The function calls \override and may be prefaced by \once (or followed by
a \revert of the relevant property).