Custom articulation for testing

Hi everyone!

Looking at MR 2521 [1] again after 2544 has been merged, I wanted to try 
using Werner’s glyph within Harm’s new side-articulation feature. So I 
made the test code below (right now using "prall" glyph for test-testing 
purposes). Why does Lily say

“warning: do not know how to interpret articulation: bachschleifer”

?

Best, Simon


[1] https://gitlab.com/lilypond/lilypond/-/merge_requests/2521

%%%%%%%%%%%%%%%%%%%%%
\version "2.25.23"

%default-script-alist.bachschleifer =
#(set! default-script-alist
        (assoc-set! default-script-alist 'bachschleifer
                    `((script-stencil . (feta . ("prall" . "prall")))
                      (padding . 0.05)
                      (avoid-slur . around)
                      (side-axis . X)
                      (direction . ,LEFT))))
bachschleifer = #(make-articulation 'bachschleifer)

{
   \key g \minor
   \time 6/8

   \partial 8 g'8 |
   es''8.[\bachschleifer d''16 c''8]
   as''8.[\bachschleifer g''16 f''8] % \break
   des'''8.[\bachschleifer c'''16 bes''8]
   fis''8.[\bachschleifer e''16 d''8]
}