docs: def extract_tag_metadata(self, el):
          """Extract meta data."""
  
          if self.type == 'odp':
              if el.namespace and el.namespace == self.namespaces['draw'] and el.name == 'page-thumbnail':
                  name = el.attrs.get('draw:page-number', '')
                  self.additional_context = 'slide{}:'.format(name)
          super().extract_tag_metadata(el)