code: def document_url(self):
          
          if '_id' not in self or self['_id'] is None:
              return None
  
          # handle design document url
          if self['_id'].startswith('_design/'):
              return '/'.join((
                  self._database_host,
                  url_quote_plus(self._database_name),
                  '_design',
                  url_quote(self['_id'][8:], safe='')
              ))
  
          # handle document url
          return '/'.join((
              self._database_host,
              url_quote_plus(self._database_name),
              url_quote(self['_id'], safe='')
          ))
docs: Constructs and returns the document URL.
  
          :returns: Document URL