KEY_BITS replaces UNSPEC which caused internal implementation problems. It is used by a redesigned KID {(kid)} to provide economical identification of keys.

KEY_BITS(0;K==>c,((4,v),(n,kbits));) returns kbits, a value that depends on the key K. Different keys that exist in slots at one time produce different kbits values.

If KEY_BITS(0,K1==>0,((4,v1),(n1,kb1))) and
KEY_BITS(0,K2==>0,((4,v2),(n2,kb2))) then:

See (p3,ik) about why you should not use this key.