Collect NoteColumns, and as soon as there are two or more, put them in a NoteCollision object.
This engraver creates the following layout objects: NoteCollision.
Collision_engraver is part of contexts: DrumStaff, GregorianTranscriptionStaff, MensuralStaff, Staff, TabStaff and VaticanaStaff
This page is for LilyPond-2.6.6 (stable-branch).