> I am trying to attach a footnote to the center of a glissando as > pictured below.
In case you don't mean "footnote" but rather "automatically rotated word 'gliss.' under the glissando line", have a look at https://lists.gnu.org/archive/html/lilypond-user/2016-06/msg00422.html This might also give you hints how to write a Scheme function of your own that is tailored to your needs. Werner
