Is there a way to circle around tab numbers?

[Devin Ulibarri]

Hi all,

I see that there is a way to circle around note heads, but I would like
to circle around fret numbers. Ultimately, I would like the string line
to be hidden from the space within the circle as well to emphasize the
number. I want to use this for pedagogical reasons. (If this description
needs further explanation, please let me know)

I see this code for the note heads:

http://lilypond.org/doc/v2.19/Documentation/snippets/editorial-annotations#editorial-annotations-drawing-circles-around-note-heads

circle =
\once \override NoteHead.stencil = #(lambda (grob)
    (let* ((note (ly:note-head::print grob))
           (combo-stencil (ly:stencil-add
               note
               (circle-stencil note 0.1 0.8))))
          (ly:make-stencil (ly:stencil-expr combo-stencil)
            (ly:stencil-extent note X)
            (ly:stencil-extent note Y))))

{ \circle c'' }

I do not really understand this level of lilypond code very well, but I
suspect with some tweaks it could do what I need. Is anyone on this list
able to help? I would appreciate it.

Thanks,
Devin