-Music, event, and scheme functions can now be defined with optional
-arguments before mandatory arguments.
+In function arguments music, markups and Scheme expressions (as well
+as several other syntactic entities) have become mostly
+interchangeable and are told apart only by evaluating the respective
+predicate.
+
+@item
+Music functions (and their close relatives) can now be defined with
+optional arguments.
+
+@item
+For defining commands executed only for their side-effects,
+@code{define-void-function} is now available.