Of the ubiquity of markup objects

Text objects are entered either as simple strings between double quotes or as \markup blocks that can accept a variety of advanced text formatting and graphical enhancements.

As such, markup blocks may be used:

• in any TextScript object (attached to notes with -, ^ or _),
• any TextMark introduced with the \textMark keyword, or \textEndMark command, or other similar objects such as MetronomeMark introduced with \tempo,
• as standalone markup blocks, entered at the top level outside of any \score block,
• in any definition inside the \header block (e.g. title, subtitle, composer) or in some variables defined inside the \paper block such as evenHeaderMarkup for page numbers.

\markup may additionally be used for lyrics, in chord names, and as dynamics. In fact, it is possible to use \markup to customize the appearance of virtually any object, as demonstrated in this example using various methods.

\version "2.24"

%% Thanks to Aaron Hill https://lists.gnu.org/archive/html/lilypond-user/2019-01/msg00437.html

\paper {
  paper-width = 8\cm paper-height = 8\cm
}

\header {
  title = \markup "Header"
  tagline = \markup "(tagline)"
}

\markup "Top-level markup"

dyn = #(make-dynamic-script #{ \markup \text "DynamicText" #})

\score {
  <<
    \new ChordNames
    \with { majorSevenSymbol = \markup "majorSevenSymbol" }
    \chordmode { c1:maj7 }
    \new Staff {
      \tempo \markup "MetronomeMark"
      \textMark "TextMark"
      \once \override TupletNumber.text = \markup "TupletNumber"
      \tuplet 3/2 {
        \once \override NoteHead.stencil = #ly:text-interface::print
        \once \override NoteHead.text = \markup \lower #0.5 "NoteHead"
        c''8^\markup "TextScript"
        \once \override Rest.stencil = #(lambda (grob)
          (grob-interpret-markup grob #{
            \markup  "Rest"
            #}))
        r4
      }
    }
    \new Lyrics \lyricmode { \markup "LyricText" 1 }
    \new Dynamics { s1\dyn }
  >>
}