QNames in xsl:element and the like

This is somewhat dependent on my message in the joint list: https://lists.w3.org/Archives/Public/public-xsl-query/2015Sep/0127.html

 

I am wondering what should happen if all of the following is true:

 

a) processor supports serialization to XML < 5th edition

b) user creates a QName == 5th edition, but not allowed in < 5th edition

c) user does not want to / need to serialize, or just uses it in a temporary tree

 

Presently, we throw an invalid QName error. But I can also argue that the QName is valid as long as you do not serialize it. Should we allow such QNames and if so, what is the prevailing method of choice: widest union of allowed characters of all editions, or just pick any edition > 3rd?

 

This question is about node generation constructs, the other referred to question is about QNames in an XPath setting.

 

Cheers,

Abel