Abigail-II, great list. I agree with most of them
(rule #24 is just a bit odd for me). Also, I understand rule #16
but don't understand the reasoning (maybe that means I
don't understand the rule). Any chance of talking you
into expounding on that some more?
#16 is about the fact that if you reference a non-existance hash key...nothing happens. Better to use the options detailed in the OP so that "mis"-references are trapped.