The class "functionXal" is a class of functionals (typically
integrals) typically of '>functionX functions.
Since the functionX functions typically also depend on tuning
parameters, objects of this class ("functionXal") are functions
of these tuning parameters.
.Data:Directly extends class "function".
Class "function", from data part.
Class "OptionalFunction", by class "function".
Class "PossibleMethod", by class "function".
psiFunc() and the class definitions of
'>functionX and
'>psi_func which has several functionXal
slots.