Hi,
For many years, one of the clearest functional gaps in LilyPond was the limitation that voices allow only a single text spanner at a time. Very many scores of recent decades notate two musical parameters changing at the same time: a passage of string music moving ponticello -> tasto while at the same time decreasing from vibrato molto -> non vibrato, for example. Arrowed lines are the nearly universal way of notating such things, available in LilyPond as text spanners; but to allow for what now counts as newly emerged common practice, an arbitrary number of text spanners need to be allowed per voice.
Lily users have asked for the feature for a long time. Here's an example from 2009:
By 2015, the idea of spanner-id had been added to LilyPond to allow for this type of functionality. But despite the name of the property ("will spanner-id allow for ALL types of spanner to overlap?"), integration first centered on slurs and phrasing slurs. Here's a thread from 2015 with David K. working to allow an input syntax for those first two types of spanner:
At that same time in 2015, however, David N. had in fact rewritten Lily's Text_spanner_engraver to integrate spanner-id, and hence supply the missing functionality. David N.'s attachment (given later in the same thread listed above) gives the necessary code:
Last year, in May 2018, I finally integrated David N.'s alternateTextSpannerEngraver into my own work, using it to replace Lily's default Text_spanner_engraver completely. The results have been extremely good: David N.'s alternateTextSpannerEngraver performs exactly the same as the current Text_spanner_engraver but with the additional flexibility of being able to define (and use) arbitrarily many types of text spanner in a single voice.
So, it looks like David N.'s alternateTextSpannerEngraver supplies a piece of functionality that's been missing in LilyPond since inception, which is fantastic.
Question: is it now possible to replace Text_spanner_engraver with David N.'s extended implementation, in a coming public release of LilyPond?
Trevor.