docs: def check_complicance(self):
          """Check compliance with Media RSS Specification, Version 1.5.1.
  
          see http://www.rssboard.org/media-rss
          Raises AttributeError on error.
          """
          # check Media RSS requirement: one of the following elements is
          # required: media_group | media_content | media_player | media_peerLink
          # | media_location. We do the check only if any media_... element is
          # set to allow non media feeds
          if(any([ma for ma in vars(self)
                  if ma.startswith('media_') and getattr(self, ma)])
             and not self.media_group
             and not self.media_content
             and not self.media_player
             and not self.media_peerLink
             and not self.media_location
             ):
              raise AttributeError(
                  "Using media elements requires the specification of at least "
                  "one of the following elements: 'media_group', "
                  "'media_content', 'media_player', 'media_peerLink' or "
                  "'media_location'.")
  
          # check Media RSS requirement: if media:player is missing all
          # media_content elements need to have url attributes.
          if not self.media_player:
              if self.media_content:
                  # check if all media_content elements have a URL set
                  if isinstance(self.media_content, list):
                      if not all([False for mc in self.media_content if
                                  'url' not in mc.element_attrs]):
                          raise AttributeError(
                              "MediaRSSItems require a media_player attribute "
                              "if a media_content has no url set.")
                  else:
                      if not self.media_content.element_attrs['url']:
                          raise AttributeError(
                              "MediaRSSItems require a media_player attribute "
                              "if a media_content has no url set.")
                  pass
              elif self.media_group:
                  # check media groups without player if its media_content
                  # elements have a URL set
                  raise NotImplementedError(
                      "MediaRSSItem: media_group check not implemented yet.")