Gotta say, "depends on the operation" was the most unfortunate possible answer to my question, alas :-) Maybe one day we'll figure out how to make a consistent array language ;-)
Why is it unfortunate? It's entirely plausible that they've managed to pick the behavior that makes most sense for each operator. Different operators being different, it doesn't make sense to expect all to behave the same. And it would be unfortunate if the common use cases were complicated by having to code out the sensible behavior if the defaults were wrong.
Well, for what it's worth - and as mentioned by a sibling poster - most verbs, and certainly all arithmetic operators, obey a few simple rules for determining which behavior you'll get. I should have noted this, before I started whining about all the other verbs, which don't :D
