I'm surprised that zen slices accept adverbs at all.
Isn't the whole point of a zen slice to return the invocant object directly,
without looking at its elements or constructing a slice from them?
I would probably make it print an error along the lines of:
===SORRY!===
Adverbs don't make sense on a zen slice.
To get a slice of all elements, use the Whatever-star: %foo[*]:v
------> say %foo[]⏏:v
(As the title of the ticket says, Whatever-slices *also* ignore :v, so that
should be fixed of course.)
