+(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.
+
+The list of allowed glyphs and predefined bar lines can be
+found in @file{scm/bar-line.scm}.
+
+@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 rounded thin-kern thick-thickness))
+