docs: def add_url(self, *args, **kwargs):
          """Add a new url to the sitemap.
  
          This function can either be called with a :class:`UrlEntry`
          or some keyword and positional arguments that are forwarded to
          the :class:`UrlEntry` constructor.
          """
          if len(args) == 1 and not kwargs and isinstance(args[0], UrlEntry):
              self.urls.append(args[0])
          else:
              self.urls.append(UrlEntry(*args, **kwargs))