Numeric notation is built right to left. To count up from 1 to 9 uses single digits, of course. Then to go from 9 to 10, the ones place increments and rolls over, and we add the new tens digit on the left, not the right.
What does it mean to be right-to-left? If it means that least significant values are on the right side and most significant ones on the left side, then domain names are left-to-right (as opposed to numeric notation).
