Fundamental Interfaces in Document Object Model Level 2 Core

Interface Document

Interface Node

Interface NodeList

Interface NamedNodeMap

Interface CharacterData

Interface Attr

Interface Element

Interface Text

Interface Comment

For More information, please get to here: Document Object Model Core

Some extra information about IE6 and IE8(from wiki):

Internet Explorer 6
This version included DHTML enhancements, content restricted inline frames, and partial support of CSS level 1, DOM level 1, and SMIL 2.0.[27] The MSXML engine was also updated to version 3.0.

Internet Explorer 8
partially supports CSS Level 2 and DOM Level 2, with major implementation gaps and conformance issues. Almost full conformance to CSS 2.1 has been added in the Internet Explorer 8 release.[54][55]