This is a position counter of a real bit in an R memory element.
Like BitIdx, it is a counter in the ring 0 .. R::BITS. It marks a real bit in memory, and is the shift distance in the expression 1 << n. It can only be produced by applying BitOrder::at to an existing BitIdx produced by bitvec.
R: The register element that this position governs.Values of this type are required to be in the range 0 .. R::BITS. Any value not less than R::BITS makes the program invalid, and will likely cause either a crash or incorrect memory access.
This type is publicly constructible, but is only correct to do so within an implementation of BitOrder::at. bitvec will only request its creation through that trait implementation, and has no sites that can publicly accept untrusted values.