Using invalid XML tagnames as the XProperty name causes irrevocable document damage

For example, renaming a property to .unused made the class document completely unusable, without the ability to delete, edit, revert. The source of the problem is that the class is stored as XML, with the property name as a tag, like in:

<.unused>
<customDisplay></customDisplay>
<name>.unused</name>
...
</.unused>

When trying to access the document, the class is also reconstructed, but parsing the XML fails, and the exception bubbles up breaking the document loading.