XEmacs Lisp lets you mark a function or variable as @dfn{obsolete},
and indicate what should be used instead.
-@deffn Command make-obsolete function new
+@deffn Command make-obsolete function new &optional when
This function indicates that @var{function} is an obsolete function,
and the function @var{new} should be used instead. The byte compiler
will issue a warning to this effect when it encounters a usage of the
documentation. @var{new} can also be a string (if there is not a single
function with the same functionality any more), and should be a descriptive
statement, such as "use @var{foo} or @var{bar} instead" or "this function is
-unnecessary".
+unnecessary". If provided, @var{when} should be a string indicating when
+the function was first made obsolete, for example a date or a release
+number.
@end deffn
@deffn Command make-obsolete-variable variable new