Constraints on infrastructureRoot attributes

There are four attributes listed in InfrastructureRoot:

nullFlavor, realmCode, typeId and templateId.

There is a belief that they are considered "special". Their use follows rules outside the mandates of the committees when performing their design work. A very conscious decision was made to not allow these attributes to be constrained by committees because it was felt that they should not be constrained (at least not in the usual manner - you can constrain nullFlavor with the mandatory indicator, and in MIF 2.0 you can require conformance with certain templates).

However some people think this decision needs to be revisited.

The aim is to answer these questions, for each of them:

1. Why it is there? ( document rules/decision )
2. Could it be constrained in the cloned classes ( Is it allowed?)
3. Should it be constrained in the cloned classes, if allowed ( should it be?)
4. How it should be contrained in the cloned classed, if allowed (How do we do it?)