(columns ,ly:grob-array? "An array of grobs, typically containing
@code{PaperColumn} or @code{NoteColumn} objects.")
(conditional-elements ,ly:grob-array? "Internal use only.")
+ (covered-grobs ,ly:grob-array? "Grobs that could potentially collide
++with a beam.")
(direction-source ,ly:grob? "In case @code{side-relative-direction} is
set, which grob to get the direction from.")