I gather that the point in your Re^8: Getting an unknown error (foreach $1 breaks m//atch) is that "it's just not possible to warn about all the weird things one might do; at some point one must fall back upon common sense."

OK; I agree with that, but I've found nothing, nor have you cited anything, that says or suggests it's "weird" to use $n as an iterator. A very succinct clarification is possible: "(I)t's possible, but unwise, to use $n as an iterator."

Think of the frequency with which the perlvar warns "See Performance issues...." or, more generally, that perldocs take the space to observe something on the order of Such-and-such a use of (function) produces undefined results. The cost of this clarification is trivial.