+1 to Ned's explanation. His note crossed mine in the posting
queue and basically address different parts of the issue.
However, one mini-correction that, IMO, just strengthens both of
our points...
Actually, RFC 20 says, in its very first sentence, "...standard
7-bit ASCII embedded in an 8 bit byte whose high order bit is
always 0". Unless I'm missing something, that is a mapping
from a CCS (although ASCII defined those integers in Column/Row
form rather than as single integers) and a CES.
Yep, it's essentially a CES. The only thing missing is the
definition of the US-ASCII charset name.
So, possibly
modulo references to different versions of ASCII (I don't have
time to check whether the Charset definition for US-ASCII points
to the same version of US-ASCII that RFC 20 does), RFC 20 and
US-ASCII are more than just "essentially" the same".
The CCSs appear identical to me. There may be some subtle difference in how
some control is defined in the ANSI documents versus RFC 20, but that's getting
pretty picky.
Ned