[anaphor]

Yep that occurred to me after I posted this, but I believe it should be possible to exclude variable variables from this at the cost of a runtime error if you try to use them in a closure. Someone else pointed out to me that PHP has other ways of messing with variables as well and that it would require full evaluation to determine all of them, so maybe it "makes sense", but only because of the extremely dynamic nature of variables in PHP.