This type is equivalent in purpose, but superior in functionality, to Range<BitPtr<M, T, O>>. If the standard library stabilizes Step, the trait used to drive Range operations, then this type will likely be destroyed in favor of an impl Step for BitPtr block and use of standard ranges.
Like Range, this is a half-open set where the low bit-pointer selects the first live bit in a span and the high bit-pointer selects the first dead bit after the span.
This type is not capable of inspecting provenance, and has no requirement of its own that both bit-pointers be derived from the same provenance region. It is safe to construct and use with any pair of bit-pointers; however, the bit-pointers it produces are, necessarily, unsafe to use.
BitPtr is required to be repr(packed) in order to satisfy the BitRef size optimizations. In order to stay minimally sized itself, this type has no alignment requirement, and reading either bit-pointer may incur a misalignment penalty. Reads are always safe and valid; they may merely be slow.
This takes the same type parameters as BitPtr, as it is simply a pair of bit-pointers with range semantics.