I must indeed have specified a range without intending to do so.

But in:

<KBD>tr/,()@+~#$%^&*-{}[]<>\/\|//s;</KBD>

. . . I don't see a range clearly targeting<kbd> A-Z </kbd>or<kbd> a-z</kbd>. And yet, characters in the range<kbd> a-z </kbd>were among those "squashed".

Update -- Coltsfoot's answer has explained this. Thanks kindly.