[kazinator]

The type tag is to be "parsed out" in some implementation specific way. For instance, we first look at the LSB of the Lisp value. If we find a 0 there, then it's a pointer; we dereference the pointer into some heap record, where we retrieve a second-level type tag. Except that, perhaps, if the whole thing is 0 bits, then it's nil; we must not chase that as a pointer. And we find a 1 in in the LSB, then perhaps we look at other surrounding bits for the type. All of this examination of bits with irregularities and cases looks like parsing.