ctext-non-standard-encodings-alist

ctext-non-standard-encodings-alist is a variable defined in `mule.el'.
Its value is

(("big5-0" big5 2 big5)
 ("ISO8859-14" iso-8859-14 1 latin-iso8859-14)
 ("ISO8859-15" iso-8859-15 1 latin-iso8859-15)
 ("gbk-0" gbk 2 chinese-gbk)
 ("koi8-r" koi8-r 1 koi8-r)
 ("microsoft-cp1251" windows-1251 1 windows-1251))

Documentation:
Alist of non-standard encoding names vs the corresponding usages in CTEXT.

It controls how extended segments of a compound text are handled
by the coding system `compound-text-with-extensions'.

Each element has the form (ENCODING-NAME CODING-SYSTEM N-OCTET CHARSET).

ENCODING-NAME is an encoding name of an "extended segment".

CODING-SYSTEM is the coding-system to encode (or decode) the
characters into (or from) the extended segment.

N-OCTET is the number of octets (bytes) that encodes a character
in the segment. It can be 0 (meaning the number of octets per
character is variable), 1, 2, 3, or 4.

CHARSET is a character set containing characters that are encoded
in the segment. It can be a list of character sets.

On decoding CTEXT, all encoding names listed here are recognized.

On encoding CTEXT, encoding names in the variable
`ctext-non-standard-encodings' (which see) and in the information
listed for the current language environment under the key
`ctext-non-standard-encodings' are used.