\version "2.22.1"

\paper  {
  print-first-page-number = ##t
  indexItemMarkup = \markup{ \fontsize #1 \fill-with-pattern #1 #RIGHT . 
                             \line { \override #'(line-width . 24) 
                                     \fontsize #1 \fill-with-pattern #1 #RIGHT . 
                                     \concat { "Exercise " \fromproperty #'index:exnum } \null 
                                     \fromproperty #'index:text } 
                             \fromproperty #'index:page
  }
}

\include "dual-index-dev.ily"

\indexItem "Top" "Top" 0  \markup "Top Level"  { c' }
\markup { \save-page-refs \unsorted "Sav0" }

\book {
  \paper  {
    first-page-number = 101
  }
  \indexItem "No.1" "No.1" 1  \markup "Number 1"  { e' }
  \markup { \save-page-refs \unsorted "Sav1" }
}

\book {
  \paper  {
    first-page-number = 201
  }
   \indexItem "No.2" "No.2" 2  \markup "Number 2"  { g' }
   \markup { \save-page-refs \unsorted "Sav2" }
}

\indexItem "No.3" "No.3" 3  \markup "Number 3"  { c'' }

\indexTitle "Exercise Index"
\markuplist { \index \unsorted }