As above, my bad. I meant that it is fully coimpatible with "8 bit ASCII", 8 bit code in which the lower 128 code points are as defined in ASCII, and the upper 128 code points are treated opaquely.
Probably as bad as well: ASCII (more exactly the US version of the ISO 646 standard) is a 7-bit charset, and says nothing about possible upper bits... So it defines only code units between 0 and 127, and no mapping for larger code units outside of this range, or the usage of other bits. ASCII can be used within more complex encodings, with or without an offset (see ISO 2022's usage of ASCII for example).
