This enum partitions a bit-slice into its head- and tail- edge bit-slices, and its interior body bit-slice, according to the definitions laid out in the module documentation.
It fragments a BitSlice into smaller BitSlices, and allows the interior bit-slice to become ::Unaliased. This is useful when you need to retain a bit-slice view of memory, but wish to remove synchronization costs imposed by a prior call to .split_at_mut() for as much of the bit-slice as possible.
Option?The Enclave variant always contains as its single field the exact bit-slice that created the Enclave. As such, this type is easily replaceäble with an Option of the Region variant, which when None is understood to be the original.
This exists as a dedicated enum, even with a technically useless variant, in order to mirror the shape of the element-domain enum. This type should be understood as a shortcut to the end result of splitting by element-domain, then mapping each PartialElement and slice back into BitSlices, rather than testing whether a bit-slice can be split on alias boundaries.
You can get the alternate behavior, of testing whether or not a bit-slice can be split into a Region or is unsplittable, by calling .bit_domain().region() to produce exactly such an Option.