Dear Fred,
Some additional comments -- after some thought, it seems to me that the APL2 designers wanted to make nested arrays do more than just encapsulate arbitrary arrays. My box/unbox do that well. APL allows operations over an ARRAY of data rather than piece by piece. That is the APL philosophy. I think that the way they implemented nested arrays in APL2 provides greater power when trying to perform operations over the entire NESTED array. My box/unbox cannot do that at all!
So, we have two benefits of nested arrays. One is to encapsulate or group dissimilar arrays. The other is to perform operations over nested, in addition to regular, arrays. In order to support the greater functionality, they had to make the encapsulation feature irregular.
Given my experience with APL and not APL2, my mind doesn't yet consider nested arrays in operations. But I have long needed the ability in APL to group dissimilar but related arrays. Given where my mind is, APL is fine, I just need the ability to group arrays. Using APL2's ⊂ and ⊃ with my functions provides what I think I need. Having real ⊂ and ⊃ will come in handy if I ever get there.
Thanks.
Blake