One minor correction:

And $hash{"key"} is the same as $hash{key} if "key" is just letters, numbers, and underscores.

I was worried that I didn't get that quite right and for good reason, too. $hash{"012"} is different than $hash{012} which is actually the same as $hash{"10"} since 012 (octal) == 10 (decimal). I worry there may be other special cases as well.

Also, on slightly old versions of Perl, things like $hash{time} will get you a warning because, on even older versions of Perl, that meant $hash{time()} and we needed a transition period before it could unambiguously mean $hash{"time"} like it does now.

        - tye (but my friends call me "Tye")