code: function append(element, content) {
    if (isElement(content)) {
      element.appendChild(content);
    } else {
      const div = document.createElement('div');
      div.innerHTML = content || '';
  
      while (div.firstChild) {
        element.appendChild(div.firstChild);
      }
    }
  }
docs: append
  
  @param {Object} element
  @param {*}      content
  
  @return undefined