IE9 latest Platform Preview Build includes two great interoperable features for working with DOM “DOM Traversal and Element Traversal” — which provide web developers with simple, flexible, and fast ways of traversing through a document using the same markup across browsers. These features come in the form of flat enumeration, simplifying DOM tree to an iterative list, and filtering which enables you to tailor the set of nodes you traverse.
Without these features, finding an element of interest on a page requires you to do one or more depth-first traversals of the document using firstChild and nextSibling. This’s usually accomplished with complex code that runs slowly. With DOM and Element Traversal features, there’re new and better ways of solving the problem.
For Best Practices: DOM Traversal