(length ,ly:moment? "The duration of this music")
(length-callback ,procedure? "How to compute the duration of this music. This property
can only be defined as initializer in @file{define-music-types.scm}.")
- (internal-class-name ,string? "C++ class to use for this Music object")
(name ,symbol? "Name of this music object")
(numerator ,integer? "numerator of a time signature")
(once ,boolean? "Apply this operation only during one time step?")