On the tangential question in the post:

"The specification describes bits as combinations of 0, 1, and x, but also sometimes includes (0) and (1). I’m not sure what the parenthesized versions mean"

the answer is that the (0) and (1) are should-be-zero and should-be-one bits: if you set them wrongly then you get CONSTRAINED UNPREDICTABLE behaviour where the CPU might UNDEF, NOP, ignore that you set the bit wrongly, or set the destination register to garbage. In contrast, plain 0 and 1 are bits that have to be that way to decode to this instruction, and if you set them to something else then the decode will take you to some other instruction (or to UNDEF) instead.