DOM 2 Traversal support

To meet the .Net behaviour in modern browsers. We could also use [ScriptName] since NextSibling etc. is a IE8 only thingy, see:
http://www.quirksmode.org/dom/w3c_traversal.html

from http://www.w3.org/TR/ElementTraversal/#introduction
"The DOM Level 1 Node interface defines 11 node types, but most commonly authors wish to operate solely on nodeType 1, the Element node. Other node types include the Document element and Text nodes, which include whitespace and line breaks [and comments]. DOM 1 node traversal includes all of these node types..."