Cross-staff chords – beaming problems workaround

Sometimes it is better to use stems from the upper staff for creating cross-staff chords, because no problems with automatic beam collision avoidance then arise. If the stems from the lower staff were used in the following example, it would be necessary to change the automatic beam collision avoidance settings so that it doesn't detect collisions between staves using \override Staff.Beam.collision-voice-only = ##t

\version "2.24"

\new PianoStaff <<
  \new Staff = up
    \relative c' {
      <<
        { r4
          \override Stem.cross-staff = ##t
          \override Stem.length = #19 % this is in half-spaces,
              % so it makes stems 9.5 staffspaces long
          \override Stem.Y-offset = #-6 % stems are normally lengthened
              % upwards, so here we must lower the stem by the amount
              % equal to the lengthening - in this case (19 - 7) / 2
              % (7 is default stem length)
          e e e }
        { s4
          \change Staff = "bottom"
          \override NoteColumn.ignore-collision = ##t
          c, c c
        }
      >>
    }
  \new Staff = bottom
    \relative c' {
      \clef bass
      \voiceOne
      g8 a g a g a g a
    }
>>