Raised on 2013-01-18
By Richard Ishida

3.9 Language Tag Characters, U+E0000..U+E007F
https://www.w3.org/TR/2013/NOTE-unicode-xml-20130124/#Language

"Problems when used in markup: These characters duplicate information that can be expressed in markup."

Actually, now that we have BCP 47, they are also no longer adequate to the task, since they are limited in scope.

Also, we don't appear to mention that they are deprecated by Unicode. I think we should.