When we display the set of dependencies for an IG manually, we generally provide some text that explains the reason for the dependency and how the referenced IG is used.  We're contemplating being able to generate this portion of the specification automatically (to ensure it's a) present; b) complete and c) rendered consistently.  To do that, we need a standard place to put the text.  Could be extension or core element, but my leaning is that it makes sense as 0..1 in core.