+A list of possible target alignment objects may be specified. If
+some of the objects are invisible at that point due to the setting
+of @code{break-visibility} or the explicit visibility settings for
+keys and clefs, the rehearsal mark or bar number is aligned to the
+first object in the list which is visible. If no objects in the
+list are visible the object is aligned to the bar line. If the bar
+line is invisible the object is aligned to the place where the bar
+line would be.
+
+@lilypond[verbatim,quote,relative=1]
+e1
+% the RehearsalMark will be centered above the Key Signature
+\override Score.RehearsalMark #'break-align-symbols = #'(key-signature clef)
+\key a \major
+\clef treble
+\mark "↓"
+e
+% the RehearsalMark will be centered above the Clef
+\set Staff.explicitKeySignatureVisibility = #all-invisible
+\override Score.RehearsalMark #'break-align-symbols = #'(key-signature clef)
+\key a \minor
+\clef bass
+\mark "↓"
+e,
+@end lilypond
+