A mask is read with bit operations, and those coerce: a null reads as the
empty mask, an object as zero. Every answer taken from a mask is a musical
claim — which form a key stands in, whether its signature is its own, which
system it belongs to — so a value that is not a mask has to be refused rather
than answered, and it is refused in one place so the answers cannot disagree
about what a mask is.
Require a twelve-bit mode mask, and return it.
A mask is read with bit operations, and those coerce: a
nullreads as the empty mask, an object as zero. Every answer taken from a mask is a musical claim — which form a key stands in, whether its signature is its own, which system it belongs to — so a value that is not a mask has to be refused rather than answered, and it is refused in one place so the answers cannot disagree about what a mask is.