I read a standard program, and can not understand this sentance

ABYTE VAR BYTE
INDEX VAR BYTE

FOR INDEX=0 TO 7
ABYTE.0[INDEX]=1 'what the "0" follow ABYTE mean? it is not a arry?
NEXT INDEX


ABYTE.0[INDEX], ABYTE[INDEX], ABYTE(INDEX) , they are the same?



I can not found any information about that, I think it is the way to change every bit of a byte, where is the rule?

great thanks