zz: Clarification re Basic Rule, Temp Lists

[Marlene Mallicoat <MarleneM@xxxxxxxxxxxxxx>]

Hi Tuomas--

A clarification of my suggestion about temporary lists.

Any operation which is always atomic need not in principle disclose
 its inner workings.  It's only when something creates ongoing data
 structures that this is really important.

However, in *principle* it would be nice to have things keep to the
 ZZ structure "all the way down"-- that way if we ever move to a
 true ZZ virtual machine, there'll be less conversion.  And it's cleaner.

All best, Ted