code: function (node) {
              var len = nodeLength(node);
  
              if (len === 0) {
                  return true;
              } else if (!isText(node) && len === 1 && node.innerHTML === blankHTML) {
                  // ex) <p><br></p>, <span><br></span>
                  return true;
              } else if (list.all(node.childNodes, isText) && node.innerHTML === '') {
                  // ex) <p></p>, <span></span>
                  return true;
              }
  
              return false;
          }
docs: returns whether node is empty or not.
  
  @param {Node} node
  @return {Boolean}