def check_values(self, values, args):
return (values, args)<EOL>
check_values(values : Values, args : [string])
-> (values : Values, args : [string])

Check that the supplied option values and leftover arguments are
valid.  Returns the option values and leftover arguments
(possibly adjusted, possibly completely new -- whatever you
like).  Default implementation just returns the passed-in
values; subclasses may override as desired.