Existing Wording: value set - selects a set of codes from those defined by one or more code systems

Comment:

allowing mixed value sets of mixed coding systems will likely make interoperability impossible. Think about it. The combinatorial explosion happens rapidly. We have to find busines rules that would constrain what we allow e.g. alow arbitrary addition of some flavors of null but not others. The argument is made that every instirution will want to add its own codes ( a different coding system). Maybe, but then why are we pretending to be pushing for interoperability? We won't have it.