code: function nextToken(tokens, idx) {
    if (++idx >= tokens.length - 2) {
      return idx;
    }
    if ((tokens[idx].type === 'paragraph_open' && tokens[idx].tight) &&
        (tokens[idx + 1].type === 'inline' && tokens[idx + 1].content.length === 0) &&
        (tokens[idx + 2].type === 'paragraph_close' && tokens[idx + 2].tight)) {
      return nextToken(tokens, idx + 2);
    }
    return idx;
  }
docs: Helper functions