A Class.t
specifies the "class" of the advice--one of `before', `after',
or `around'. Before-advice runs before the function itself;
after-advice runs after the function itself; around-advice is wrapped
around the execution of the function itself.
(Info-goto-node "(elisp)Defining Advice")
include sig ... end
val sexp_of_t : t ‑> Sexplib.Sexp.t