def _validate_top_level(self, boxes):
<EOL>for box in boxes:<EOL><INDENT>if hasattr(box, '<STR_LIT>'):<EOL><INDENT>self._check_superbox_for_top_levels(box.box)<EOL><DEDENT><DEDENT>count = self._collect_box_count(boxes)<EOL>if '<STR_LIT>' in count and '<STR_LIT>' not in count:<EOL><INDENT>msg = ('<STR_LIT>'<EOL>'<STR_LIT>')<EOL>raise IOError(msg)<EOL><DEDENT>
Several boxes can only occur at the top level.