+ '(gap
+ length-fraction
+ maximum-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.
+
+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
+ hair-thickness
+ has-span-bar
+ kern
+ rounded
+ thin-kern
+ thick-thickness))