Adding timing marks to long glissandi

Skipped beats in very long glissandi are sometimes indicated by timing marks consisting of stems without noteheads. Such stems can also be used to carry intermediate expression markings.

If the stems do not align well with the glissando, they may need to be repositioned slightly.

\version "2.24"

glissandoSkipOn = {
  \override NoteColumn.glissando-skip = ##t
  \hide NoteHead
  \override NoteHead.no-ledgers = ##t
}

glissandoSkipOff = {
  \revert NoteColumn.glissando-skip
  \undo \hide NoteHead
  \revert NoteHead.no-ledgers
}

\relative c'' {
  r8 f8\glissando \glissandoSkipOn f4 g a |
  a8\noBeam \glissandoSkipOff a8
    r8 f8\glissando \glissandoSkipOn g4 a8 \glissandoSkipOff a8 |
  r4 f\glissando\< \glissandoSkipOn a4\f\> \glissandoSkipOff b8\! r |
}