On the BlockModel and BlockPackage principle

Some years ago Dr Darren introduced custom «BlockModel» and «BlockPackage» stereotypes to express this idea of collecting all data related to a Block in one place, with the «BlockPackage» owning one Block and related artifacts, including InstanceSpecifications assigned to UML Property.defaultValue: ValueSpecification [0..1].

However, enforcing it as a constraint 'must be .. owned by the same package that owns the outermost containing block for which the initial values are being specified' prevents sharing of data through shared InstanceSpecifications, and in some cases - where one relies on sharing for integrity of propagated data, it can be inconvenient.

Why 'The instance specification must be unnamed' ?

Dr Darren contests the need for the InstanceSpecification to be unnamed; naming has enormous value communicating intention, as well as educational value.