docs: def _get_tag(self, url, tag, print_warn=True):
          """Check if url is available and returns given tag type
          :param url: url to content relative to base url
          :param anchor: anchor type to return
          :param print_warn: if True print warn when url is unavailable
          """
          # construct complete url
          complete_url = urljoin(self.base_url, url)
          # check if exists
          if requests.get('http:' + complete_url).ok:
              # construct tag
              if tag == 'script':
                  return '<script src="{0}"></script>'.format(complete_url)
              elif tag == 'stylesheet':
                  return '<link rel="stylesheet" href="{0}">'.format(complete_url)
              else:
                  warnings.warn('Given tag is not valid')
          elif print_warn:
              warnings.warn('Url {0} not valid'.format(complete_url))
          return None