Consider allowing a collection schema within a collection

[kzu]

This was allowed in NuPattern, but for code-first it could only be represented as IEnumerable<IEnumerable>. It's a pretty rare occurrence in actual modeling, and we're back to the idea that collections of things are most typically grouped within parent elements so that they can be easily grouped/collapsed.

The same effect as this could be achieved by having an IEnumerable, where each ISomethings has a property of IEnumerable. And we make the property node visibility as Content (so that the property itself doesn't show up). This would give you the same rendering as the above model, but it would be (code and modeling wise) much more common and intuitive.