-;; todo: figure out where to put this doco:
-
-"
-Grob properties form a name space where you can set variables per
-object. Each object however, may have multiple functions. For
-example, consider a dynamic symbol, such @code{\ff} (fortissimo). It
-is printed above or below the staff, it is a dynamic sign, and it is a
-kind of text.
-
-To reflect this different functions of a grob, procedures and variables
-are grouped into so-called interfaces. The dynamic text for example
-supports the following interfaces:
-@table @code
-@item font-interface
- The glyph is built from characters from a font, hence the
-@code{font-interface}. For objects supporting @code{font-interface}, you
-can select alternate fonts by setting @code{font-style},
-@code{font-point-size}, etc.
-
-@item dynamic-interface
- Dynamic interface is not associated with any variable or function in
-particular, but this makes it possible to distinguish this grob from
-other similar grobs (like @code{TextScript}), that have no meaning of
-dynamics.
-
-@item text-interface
- This interface is for texts that are to be set using special routines
-to stack text into lines, using kerning, etc.
-
-@item general-grob-interface
- This interface is supported by all grob types.
-@end table
-"
+(ly:add-interface
+ 'rhythmic-grob-interface
+ "Any object with a rhythmic basis. Used to determine which grobs
+are interesting enough to maintain a hara-kiri staff."
+ '())
+
+(ly:add-interface
+ 'stanza-number-interface
+ "A stanza number, to be put in from of a lyrics line"
+ '())
+
+(ly:add-interface
+ 'bass-figure-interface
+ "A bass figure text"
+ '(implicit))
+
+;;; todo: this is not typesetting info. Move to interpretation.
+(ly:add-interface
+ 'tablature-interface
+ "An interface for any notes set in a tablature staff"
+ '())
+
+(ly:add-interface
+ 'vertically-spaceable-interface
+ "Objects that should be kept at constant vertical distances. Typically:
+@internalsref{VerticalAxisGroup} objects of @internalsref{Staff} contexts."
+ '())