\version "2.18.0"

allowGrobCallback =
#(define-scheme-function (parser location syms) (symbol-list?)
   (let ((interface (car syms))
         (sym (cadr syms)))
     #{
       \with {
         \consists #(lambda (context)
                      `((acknowledgers .
                          ((,interface . ,(lambda (engraver grob source-engraver)
                                            (let ((prop (ly:grob-property grob sym)))
                                              (if (procedure? prop) (ly:grob-set-property! grob sym (prop grob)))
                                              ))))
                          ))
                      )
       }
     #}))

absFontSize =
#(define-scheme-function (parser location pt)(number?)
   (lambda (grob)
     (let* ((layout (ly:grob-layout grob))
            (ref-size (ly:output-def-lookup (ly:grob-layout grob) 'text-font-size 12)))
       (magnification->font-size (/ pt ref-size))
       )))

\layout {
  \context {
    \Score
    \allowGrobCallback font-interface.font-size

    % some "global" overrides
    \override TextScript.font-size = \absFontSize #16
    \override LyricText.font-size = \absFontSize #7
    \override InstrumentName.font-size = \absFontSize #24
    \override BarNumber.font-size = \absFontSize #18
  }
}

% example Music
\paper {
  % just to make the huge instrument name fit
  left-margin = 2\cm
}

\new Staff \with {
  instrumentName = "Melodie"
  shortInstrumentName = "Mel"
} \new Voice {
  \repeat unfold 19 \relative c'' { bes4^"Hello" a c b }
  \break
  \once \override Score.BarNumber.font-size = \absFontSize 40
  \once \override TextScript.font-size = \absFontSize 30
  \once \override Score.LyricText.font-size = \absFontSize 40
  \once \override Score.LyricText.stencil =
  #(lambda (grob)
     (let* ((lyr (ly:grob-property grob 'text))
            (stil (lyric-text::print grob))
            (stil-ref (grob-interpret-markup grob (markup #:with-color red #:abs-fontsize 40 lyr))))
       ; store lyric-text stencil and lyric markup
       (ly:parser-define! parser 'lyrstil stil)
       (ly:parser-define! parser 'lyrmup lyr)
       (ly:stencil-add stil stil-ref)))
  \repeat unfold 6 \relative c'' {
    bes4^"World" a c b
  }
} \addlyrics {
  \repeat unfold 25 { B A C H }
  }
% create a markup from stored lyric stencil and markup
  #(define-markup-command (debug layout props)()
     (ly:stencil-add lyrstil (interpret-markup layout props (markup #:with-color red #:abs-fontsize 40 lyrmup))))

  \markup { \debug }