The XML & SOAP APIs are full of overrides for scenarios where some application or other is finicky. 

As for the documentation, we received your feedback item but due to an short term mishap lost your email address. Here's our reply:

Hello!

Thanks for providing feedback on InterSystems documentation. We make ongoing improvements to our content and really appreciate receiving input.

Regarding your feedback about writing an empty self-closing XML element, we have corrected the documentation. (I dug out my old test code and proved it to myself.)

We hope this addresses your input, and please feel free to be in touch if you have any follow-up questions or comments.

Sincerely,
InterSystems Documentation