It doesn't give as specific of guidance as you might expect, but search for the word WARNING in perlobj. It makes it very clear that the indirect object notation is ambiguous.

This is why Damian Conway says in his book that you should avoid the indirect object notation...

UPDATE
As came out several levels below, I had not understood the error at all. It is far more subtle...

In reply to Re (tilly) 1: Filehandles vs. Packages: And the winner is... by tilly
in thread Filehandles vs. Packages: And the winner is... by converter

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