New properties for TAXII 2.1

All,
It has been proposed that we add some properties to collections to help identify what data markings are needed / supported in this collection.  One driving aspect is with the upcoming IEP policy stuff.
It has been proposed that we add something like the following two properties:
supported_markings
required_markings
The property terms may need to be word smithed and we need to figure out how to best capture the data.  But the question right now is, should we support this functionality on collections?
If so, I will add them to the TAXII 2.1 working specification so that we can being work on what they will mean.
Bret