Intuitively, I feel that the block must add a wider scope than the expression: for the latter, the scope effect is limited to affect just $_, for the block, you can add lexical variables of your own.

Put it this way: the expression can use a "lite" scope.

caveat: I have no idea if this is actually the case!

In reply to Re^2: syntax of map operator by bart
in thread syntax of map operator by sman

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