emacs -Q
 
The character range (128 . 4194303) is bound to `self-insert-command'.
 
(single-key-description 128) gives "\200"
(single-key-description 4194303) gives "\377"
 
However, in the former case, "\200" is a string with one character,
\200. In the latter case, "\377" is a string with four characters, \,
3, 7, and 7.
 
In GNU Emacs 23.1.1 (i386-mingw-nt5.1.2600)
 of 2009-07-29 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.4)'