Square balloons

Elements of notation can be marked and named with the help of a square balloon. The primary purpose of this feature is to explain notation.

\version "2.24"

%% http://lsr.di.unimi.it/LSR/Item?id=423

\new Voice \with { \consists "Balloon_engraver" }
  \relative c''{
   \balloonGrobText #'Stem #'(3 . 4) \markup { "I'm a Stem" }
   a4
   <c, g'-\balloonText #'(-2 . -2) \markup { "I'm a note head" } c>2.
}