Dashed slurs indicating optional slurs between lyric lines

[Romel Anthony S. Bismonte]

After tooling around a bit in LilyPond, I think I may have developed 
something potentially useful for someone out there. And wouldn't you know, I 
got to it because I needed it myself! ^_^

In the songbook we use at church, the verses to the song are stacked on top 
of each other if the melody lines are similar enough. But if two notes are 
slurred in one verse and sung separately in another, they are connected with 
a dashed slur, and the lyrics align under the notes respectively. I've found 
a way to do this in LilyPond:

\version "2.10.25"
\score {
   <<
       \new Voice = "melody" \relative c' {
           c8 e8
           \voiceOne
           <<
               { d8 f8 \oneVoice }
               \new Voice {
                   \voiceTwo \hideNotes \slurDashed
                   \once \override Slur #'line-thickness = #2.5
                   d8( f8)
                   \unHideNotes
               }
           >>
           e8 g8 f8 a8
       }
       \new Lyrics \lyricsto "melody" {
           One two three four five six seven eight
       }
       \new Lyrics \lyricsto "melody" {
           One two Whee! \skip 4 that's a dashed slur!
       }
   >>
}

Essentially, it creates polyphony (as described in the Manual) where the 
dashed slur is needed, places invisible notes there, and connects those with 
a dashed slur. That way, back in the main voice, lyrics can still align 
beneath either note. I found that thickening the slur with an \override 
command worked best because an ordinary dashed slur was almost invisible on 
my screen.

Then, to align the lyrics underneath the right notes, place \skip 
instructions where you don't want words. The \skip instruction has a value 
of 4--I used that value to show that it doesn't matter how long the skip is 
in the \lyricsto context; it will skip one note opportunity.

I was going to post this on the LSR right away, and I think I might still do 
so, but wouldn't it be nicer if this could be implemented as a music 
function? Something like

\singableSlur "dashed" { d8 f8 }

Now that would be a big help for typesetting music with many similar verses.

Hope this helps someone--God knows this mailing list has been a really big 
help in my own typesetting endeavor. ^_^

Regards,
Romel