docs: def _highlight(self, content, ngrams, highlight):
          """Returns `content` with its n-grams from `ngrams` highlighted (if
          `add_class` is True) or unhighlighted.
  
          :param content: text to be modified
          :type content: `str`
          :param ngrams: n-grams to modify
          :type ngrams: `list` of `str`
          :param highlight: whether to highlight or unhighlight `ngrams`
          :type highlight: `bool`
          :rtype: `str`
  
          """
          self._add_highlight = highlight
          for ngram in ngrams:
              pattern = self._get_regexp_pattern(ngram)
              content = re.sub(pattern, self._annotate_tokens, content)
          self._ngrams_count += 1
          return content