Unable to recognize tab page

Raise code

        if video_id:
            return self.url_result(video_id, ie=YoutubeIE.ie_key(), video_id=video_id)
        # Capture and output alerts
        alert = self._extract_alert(data)
        if alert:
            raise ExtractorError(alert, expected=True)
        # Failed to recognize
        raise ExtractorError('Unable to recognize tab page')


class YoutubePlaylistIE(InfoExtractor):
    IE_DESC = 'YouTube.com playlists'
    _VALID_URL = r'''(?x)(?:
                        (?:https?://)?
                        (?:\w+\.)? '''

Comment explaining raise

Failed to recognize