Handle ``type`` statement.

        Built-in types are handled by one of the specific type
        callback methods defined below.

def type_stmt(self, stmt, p_elem, pset):
        """Handle ``type`` statement.

        Built-in types are handled by one of the specific type
        callback methods defined below.
        """
        typedef = stmt.i_typedef
        if typedef and not stmt.i_is_derived: # just ref
            uname, dic = self.unique_def_name(typedef)
            if uname not in dic:
                self.install_def(uname, typedef, dic)
            SchemaNode("ref", p_elem).set_attr("name", uname)
            defst = typedef.search_one("default")
            if defst:
                dic[uname].default = defst.arg
                occur = 1
            else:
                occur = dic[uname].occur
            if occur > 0: self.propagate_occur(p_elem, occur)
            return
        chain = [stmt]
        tdefault = None
        while typedef:
            type_ = typedef.search_one("type")
            chain.insert(0, type_)
            if tdefault is None:
                tdef = typedef.search_one("default")
                if tdef:
                    tdefault = tdef.arg
            typedef = type_.i_typedef
        if tdefault and p_elem.occur == 0:
            p_elem.default = tdefault
            self.propagate_occur(p_elem, 1)
        self.type_handler[chain[0].arg](chain, p_elem)