Strict test for 'true' value test. If multiple args are provided it will
        test them all.
            ISTRUE:true

        %{ISTRUE:true} -> 'True'

def istrue(self, *args):
        """Strict test for 'true' value test. If multiple args are provided it will
        test them all.
            ISTRUE:true

        %{ISTRUE:true} -> 'True'
        """
        def is_true(val):
            if val is True:
                return True
            val = str(val).lower().strip()
            return val in ('true', 'yes', '1')
        return all(self._arg_factory(is_true, args))