my is a valid attribute name, so : my is presumed to be an attribute.

$d is not a valid attribute name, so : $d is taken to be the else expression of the conditional.

Thanks for the explanation! (I eventually figured out that it must be something like that, and updated my post; but probably it was after you had already begun yours.)

Since the word ‘attribute’ does not occur in perlop or perlsyn, and since no other punctuation mark requires a visit to perlfunc to figure out how it parses, I wonder if it might be appropriate for the precedence table to mention this unexpected (by me) interaction?

Note that conditionally executing my is officially undefined behaviour.

Good to know, thanks. Is there any unified list of officially undefined things? I know, for example, by luck, that $i++ + ++$i can officially do whatever it wants, but I had no idea about this; who knows what other corner cases I'm missing?