code: function getHeaderContent(tokens, type, markup) {
    if (tokens[1].children.length === 0) {
      tokens[1].children.push(getEmptyText());
    } else if (tokens[1].children[0].type !== 'text') {
      tokens[1].children.unshift(getEmptyText());
    }
    const content = changeText(tokens[1].children, markup);
    return {
      type,
      content,
      length: getTokensLength(content)
    };
  }
docs: getHeaderContent - Function create content for header-token
  
  @param tokens
  @param type
  @param markup
  @returns {{type: *, content}}