\version "2.18.2"

#(define-public (string-or-markup-or-boolean? e)
  (or (string? e) (markup? e) (boolean? e)))

#(define (double-rehearsalmark-stencil grob)
  (let*
   ((grobs-event (ly:grob-property grob 'cause '()))
    (left-label (ly:event-property grobs-event 'left-label))
    (right-label (ly:event-property grobs-event 'right-label))
    (gap (ly:grob-property grob 'gap 1.4)))
   (case (ly:item-break-dir grob)
    ((-1)
     (if (boolean? left-label) empty-stencil
      (grob-interpret-markup grob
       (make-right-align-markup left-label))))
    ((1)
     (if (boolean? right-label) empty-stencil
      (grob-interpret-markup grob
       (make-left-align-markup right-label))))
    (else
     (if (boolean? left-label)
      (grob-interpret-markup grob
       (if left-label
        (make-center-align-markup right-label)
        (make-left-align-markup right-label)))
      (if (boolean? right-label)
       (grob-interpret-markup grob
        (if right-label
         (make-center-align-markup left-label)
         (make-right-align-markup left-label)))
       (ly:stencil-add
        (ly:stencil-translate
         (grob-interpret-markup grob
          (make-right-align-markup left-label))
         (cons (* -0.5 gap) 0.0))
        (ly:stencil-translate
         (grob-interpret-markup grob
          (make-left-align-markup right-label))
         (cons (* 0.5 gap) 0.0)))))))))

doubleMark =
#(define-music-function
  (parser location left-string right-string)
  (string-or-markup-or-boolean? string-or-markup-or-boolean?)
  (if (and (boolean? left-string) (boolean? right-string))
   (ly:warning "~a \\doubleMark - at least one string or markup required" location))
  (make-music 'SequentialMusic
   'elements (list
    (make-music 'ContextSpeccedMusic
     'context-type 'Score
     'element
      (make-music 'OverrideProperty
       'symbol 'RehearsalMark
       'grob-value double-rehearsalmark-stencil
       'grob-property-path (list 'stencil)
       'pop-first #t
       'once #t))
    (make-music 'ContextSpeccedMusic
     'context-type 'Score
     'element
      (make-music 'OverrideProperty
       'symbol 'RehearsalMark
       'grob-value #f
       'grob-property-path (list 'self-alignment-X)
       'pop-first #t
       'once #t))
    (make-music 'ContextSpeccedMusic
     'context-type 'Score
     'element
      (make-music 'OverrideProperty
       'symbol 'RehearsalMark
       'grob-value `#(,(not (boolean? left-string))
                      #t
                      ,(not (boolean? right-string)))
       'grob-property-path (list 'break-visibility)
       'pop-first #t
       'once #t))
    (make-music 'MarkEvent
     'label #f
     'left-label (if (string? left-string)
                  (make-simple-markup left-string)
                  left-string)
     'right-label (if (string? right-string)
                   (make-simple-markup right-string)
                   right-string)
     'origin location))))


{
  \mark \markup { \box \bold \fontsize #2 A}
  \repeat volta 2 { s1*4 | \break }
  \alternative { { s1*4 \break} { s1*4
  \once\override Score.RehearsalMark.break-visibility = #end-of-line-visible
  \once\override Score.RehearsalMark.self-alignment-X = #RIGHT
  \doubleMark 
  \markup {\hspace #8 \italic "fine"}
  \markup { \box \bold \fontsize #2 B} |
  \bar "||" \break} }
  s1*4\break 
  s1*4
  \once \override Score.RehearsalMark #'direction = #DOWN
  \once \override Score.RehearsalMark.break-visibility = #end-of-line-visible
  \once \override Score.RehearsalMark.self-alignment-X = #RIGHT
  \mark \markup {\hspace #8 \bold "D.C. al 2nd Ending"}
  \bar "||" \break
}