A Slot is an object which provides the behavior of the binding of a noun. "
&" in the E language allows working with slots.
A slot can also be considered a zero-dimensional collection, i.e. one which has exactly one element.
Returns the current value of this slot.
Sets the current value to the (possibly coerced) provided value, if appropriate for this type of slot; throws if not allowed.
Note that final implies read-only, but read-only does not imply final.
Returns a facet allowing get/0 but not put/1.