#(set-default-paper-size "a6")

#(define-markup-command (toc-line layout props label text)
  (symbol? markup?)
  (interpret-markup layout props
   (markup #:fill-line (text #:page-ref label "8" "?"))))

\book {
  \markup \huge \fill-line { \null Title Page \null }

  \pageBreak

  \label #'toc
  \markup \column {
    \large \fill-line { \null Table of contents \null }
    \toc-line #'toc "Table of contents"
    \toc-line #'firstScore "First Score"
    \toc-line #'markA "Mark A"
    \toc-line #'markB "Mark B"
    \toc-line #'markC "Mark C"
    \toc-line #'unknown "Unknown label"
  }

  \pageBreak

  \label #'firstScore
  \score {
    \new Staff \relative c' {
      c2 c
      \mark \markup {
        A (page \concat { \page-ref #'markA "0" "?" ) }
      } \label #'markA
      c2 c
      \pageBreak
      \mark "B" \label #'markB
      d2 d
      d2 d
      \once \override Score.RehearsalMark.break-visibility =
        #begin-of-line-invisible
      \mark "C" \label #'markC
    }
    \header { piece = "First score" }
  }
}