This is more a hint than a bug, and possibly it's already known
- sorry then. The report concerns the documentation of $^W.
Currently, it implies that $^W=0 disables -w, in other words,
that $^W and -w are synonyms. But this is not completely true
because of the two phases precompilation and runtime - a $^W
assignment outside BEGIN scopes does NOT affect warnings produced
by the compiler, e.g. "Variable used only once."
So I propose to simply add a more detailed explanation where
$^W influences which warnings.