DocumentTraversal DOM 2 TR  Contains methods that create iterators and tree-walkers to traverse a node and its children in document order.
 NodeIterator DOM 2 TR  Allows you to iterate over the members of a list of the nodes in a subtree of the DOM, in document order.
 TreeWalker DOM 2 TR  Represents the nodes of a document subtree and a position within them.
 NodeFilter DOM 2 TR  Filters are objects that know how to "filter out" nodes.