Just playing around with the Euromath Eclipse plugin:
First, I tried creating a new XML file using the wizard: However, "Next" did absolutely nothing.
Then I tried creating an empty file: The editor fails to initialize (document not well formed)
Now I've added a single node, and the editor fails with "does not allow null namespace":
<math></math>
So I added the namespace, and got got a dialog box asking me for tree representation / wysiwyg representation. I did not select tree and guess what? It failed again, this time complaining the that there is no content:
<math xmlns="http://www.w3.org/1998/Math/MathML" ></math>
However, the tree representation worked fine.
I'll keep playing with it and maybe report more findings.