This will perform a logical Exclusive OR as follows:
Take num1 and EOR it with num2, write the result to var.
A = B EOR 255
eor(A, B, &FF)
EOR inverts the specified bits. It is algorythmically regular in that a byte, when EORed with a specific value, can be restored by EORing it with that same value again.
The difference between this and not() is that you can control which bits you with to invert, while not() inverts them all.
A 'not' operation is equivalent to exclusive ORing with all bits set. Both of these commands perform the exact same action:
eor(A, B, -1)
Because so much PC-related software uses the parlance "Xor", this version is also accepted by the Windows interpreter.