It probably made the test suite easier to manage at the time.

>
> My questions please,
> What would, end user applications do with such XML documents?

The same as with any other XML documents.

Note that if an attribute uses a different script from the contents of
the element, and that also differs from the script of the container,
there's no way to mark that in XML in a standard interoperable way. So
there can sometimes be rendering problems, because script and language
information is needed in some cases to get rendering right.

But there's nothing special about the contents of that attribute that i
see at first glance.