If this is True, allow typecode to be substituted
        for "self" typecode.

def checkSubstitute(self, typecode):
        '''If this is True, allow typecode to be substituted
        for "self" typecode.
        '''
        if not isinstance(typecode, ElementDeclaration): 
            return False

        try:
            nsuri,ncname = typecode.substitutionGroup
        except (AttributeError, TypeError):
            return False

        if (nsuri,ncname) != (self.schema,self.literal):
            # allow slop with the empty namespace 
            if not nsuri and not self.schema and ncname == self.literal:
                 return True

            return False

        sub = GED(self.schema, self.literal)
        if sub is None or sub is not typecode:
            return False

        return True