XML tree annotator (and editor)

[gusl]

I'm looking for a program that works with XML documents, and will let you:

(1) visualize trees/graphs encoded in XML formats
(2) add/edit annotations on the elements (in particular, nodes) of this tree (i.e. create a new XML tag next to element)

Any ideas?

An XML editor (here's a fancy one) with a tree-view (no pun intended) would almost satisfy (2), but it would be annoying to use another program for visualizing the tree.

"maybe suitable" list:
CLaRK system
Cadixe

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UPDATE: if I'm going to settle for an XML editor, this page is useful.