MS XML Notepad 2007 <BR><BR>edit: just to clarify, this is an xml file editor that has a tree view pane on the left. You can right click and expand the whole tree, or leave it collapsed.

XML, the extensible Markup Language, was initiated in 1998 as a computer language designed to ease interchange of data online. XML.org is headed by the World Wide Web Consortium (WC3).