27.6 Unibyte and Multibyte Non-ASCII characters
When multibyte characters are enabled, character codes 0240 (octal)
through 0377 (octal) are not really legitimate in the buffer. The valid
non-ASCII printing characters have codes that start from 0400.
If you type a self-inserting character in the range 0240 through
0377, or if you use C-q to insert one, Emacs assumes you
intended to use one of the ISO Latin-n character sets, and
converts it to the Emacs code representing that Latin-n
character. You select which ISO Latin character set to use
through your choice of language environment
If you do not specify a choice, the default is Latin-1.
If you insert a character in the range 0200 through 0237, which
eight-bit-control character set, it is inserted
literally. You should normally avoid doing this since buffers
containing such characters have to be written out in either the
raw-text coding system, which is usually
not what you want.