+(ly:add-interface
+ 'ambitus-interface
+ "The line between note heads for a pitch range."
+ '(gap note-heads thickness))
+
+(ly:add-interface
+ 'bar-line-interface
+ "Print a special bar symbol. It replaces the regular bar
+symbol with a special symbol. The argument @var{bartype}
+is a string which specifies the kind of bar line to print.
+Options are @code{|}, @code{:|}, @code{|:}, @code{:|:}, @code{:|.|:},
+@code{:|.:}, @code{.}, @code{||}, @code{|.}, @code{.|}, @code{.|.},
+@code{|.|}, @code{:}, @code{dashed}, @code{'} and @code{S}.
+
+These produce, respectively, a normal bar line, a right repeat, a left repeat,
+a thick double repeat, a thin-thick-thin double repeat,
+a thin-thick double repeat, a thick bar, a double bar, a start bar,
+an end bar, a thick double bar, a thin-thick-thin bar,
+a dotted bar, a dashed bar, a tick as bar line and a segno bar.
+
+In addition, there is an option
+@code{||:} which is equivalent to @code{|:} except at line
+breaks, where it produces a double bar (@code{||}) at the
+end of the line and a repeat sign (@code{|:}) at the
+beginning of the new line.
+
+For segno, @code{S} produces a segno sign except at line breaks,
+where it produces a double bar (@code{||}) at the
+end of the line and a segno sign at the beginning of the new line.
+@code{|S} is equivalent to @code{S} but produces a simple bar line
+(@code{|}) instead of a double bar line (@code{||}) at line breaks.
+@code{S|} produces the segno sign at line breaks and starts the following
+line without special bar lines.
+
+@code{S|:} and @code{:|S} are used for repeat/segno combinations that are
+separated at line breaks. Alternatively, @code{.S|:} and @code{:|S.}
+may be used which combine repeat signs and segno at the same line in
+case of a line break. @code{:|S|:} is a combination of a left repeat
+(@code{:|}), a segno (@code{S}) and a right repeat @code{|:} which
+splits before the segno at line breaks; @code{:|S.|:} splits after
+the segno sign.
+
+If @var{bartype} is set to @code{empty} then nothing is
+printed, but a line break is allowed at that spot.
+
+@code{gap} is used for the gaps in dashed bar lines."
+ '(allow-span-bar bar-extent gap glyph glyph-name has-span-bar
+ hair-thickness kern thin-kern thick-thickness))
+