function domTraverseElements(node, callback) {
  var traverser = new DomTraverser(callback);
  traverser.run(node);
}
Traverses the element nodes in the DOM section underneath the given
node and invokes the given callback as a method on every element
node encountered.

@param {Element} node  Parent element of the subtree to traverse.
@param {Function} callback  Called on each node in the traversal.