* While the syntax of ADD, ADC and SBC instructions all explicitely mention the A register, the SUB instruction does not mention it.
* The 16-bit commands ADD HL,ss, ADC HL,ss and SBC HL,ss exist but not the command SUB HL,ss.
* All PUSH and POP instructions utilize a 16-bit operand and the high-order byte is always pushed first and popped last. PUSH HL is PUSH H then L. POP HL is POP L then H.
* INI/IND/INIR/INDR decrease B after storing the byte from the hardware port into memory. And OUTI/OUTD/OTIR/OTDR decrease B before sending the memory byte to the hardware port. [https://www.cpcwiki.eu/forum/programming/z80-documentation-errors/ Source]
* When an LDxR / CPxR / INxR / OTxR instruction is interrupted, the interrupt handler sees some flags in a different state. [https://github.com/hoglet67/Z80Decoder/wiki/Undocumented-Flags#interrupted-block-instructions Source]