The Z8000 has sixteen 16 bit registers, numbered 0 to 15. You can refer to different sized groups of registers by register number, with the prefix r for 16 bit registers, rr for 32 bit registers and rq for 64 bit registers. You can also refer to the contents of the first eight (of the sixteen 16 bit registers) by bytes. They are named rln and rhn.
byte registers
rl0 rh0 rl1 rh1 rl2 rh2 rl3 rh3 rl4 rh4 rl5 rh5 rl6 rh6 rl7 rh7
word registers
r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 r14 r15
long word registers
rr0 rr2 rr4 rr6 rr8 rr10 rr12 rr14
quad word registers
rq0 rq4 rq8 rq12