ShimiShimson's solution for Tree Walker

[Szymon Adamczuk]

nextNode = function(node) {

  //...Code goes here to walk to the next node...

  if (node.firstChild) return node.firstChild;

  if (node.nextSibling) return node.nextSibling;

  while (!node.parentNode.nextSibling) node = node.parentNode;

  return node.parentNode.nextSibling;

};