As we start to apply FMM levels and think about the notion of "normative" to terminology artifacts, the community needs to understand what sorts of changes will be permitted without consulting the community (level 4/5) or at all (normative). In some cases, these will be quite limiting - perhaps to the level of any change to the expansion. In other cases, it may be open to such a significant changes as migrating from ICD9 to ICD10 or SNOMED. Because this variability in behavior needs to be allowed, the explicit rules need to be captured at a "per valueset" level.

It may be this should be a choice of code|string so we can define a few common conformance behaviors, but also allow for a particular code system or value set to have it's own "specific/special" defined behavior

Example code system behaviors:
a) Fixed expansion
b) Expansion can increase, but no changes to existing concepts (including no overlapping/ancestor concepts)
c) Expansion can increase, but no changes to existing concepts, new overlapping/ancestor concepts are allowed
d) Existing concepts can be increased in scope (non-overlapping with existing concepts) and new concepts can be added including overlapping/ancestor concepts\\...
z) No constraints

Example value set behaviors:
a) Definition is fixed
b) Additional concepts can be introduced from the same code system, but no new code systems
c) Existing concepts can be replaced with concepts from a different code system

We need to identify what behaviors are typical/useful