code: def rng_annotation(self, stmt, p_elem):
          
          ext = stmt.i_extension
          prf, extkw = stmt.raw_keyword
          (modname,rev)=stmt.i_module.i_prefixes[prf]
          prefix = self.add_namespace(
              statements.modulename_to_module(self.module,modname,rev))
          eel = SchemaNode(prefix + ":" + extkw, p_elem)
          argst = ext.search_one("argument")
          if argst:
              if argst.search_one("yin-element", "true"):
                  SchemaNode(prefix + ":" + argst.arg, eel, stmt.arg)
              else:
                  eel.attr[argst.arg] = stmt.arg
          self.handle_substmts(stmt, eel)
docs: Append YIN representation of extension statement `stmt`.