The most important bit of the first part of your question is probably this:

More generally, a slice yields the empty list if it indexes only beyond the end of a list

And yeah, this does scream inconsistency to me!

    @a = (1)[1,0];          # @a has two elements
                            # OK, this one is fine

    # but what about these:

    @b = (1,undef)[1,0,2];  # @b has three elements
                            # where does that third element come from?

    # or we could rewrite the above B case like this
    # and still get three elements:
    @b = (1)[1,0,2];        # why three and not *TWO*?

    @a = (1)[  1,2];        # @a has no elements
                            # !?
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Great question, thanks for bringing this up.