Q.2 Enabling Multibyte Characters

You can enable or disable multibyte character support, either for Emacs as a whole, or for a single buffer. When multibyte characters are disabled in a buffer, then each byte in that buffer represents a character, even codes 0200 through 0377. The old features for supporting the European character sets, ISO Latin-1 and ISO Latin-2, work as they did in Emacs 19 and also work for the other ISO 8859 character sets.

However, there is no need to turn off multibyte character support to use ISO Latin; the Emacs multibyte character set includes all the characters in these character sets, and Emacs can translate automatically to and from the ISO codes.

By default, Emacs starts in multibyte mode, because that allows you to use all the supported languages and scripts without limitations.

To edit a particular file in unibyte representation, visit it using find-file-literally. See section M.2 Visiting Files. To convert a buffer in multibyte representation into a single-byte representation of the same characters, the easiest way is to save the contents in a file, kill the buffer, and find the file again with find-file-literally. You can also use C-x RET c (universal-coding-system-argument) and specify `raw-text' as the coding system with which to find or save a file. See section Q.9 Specifying a Coding System. Finding a file as `raw-text' doesn't disable format conversion, uncompression and auto mode selection as find-file-literally does.

To turn off multibyte character support by default, start Emacs with the `--unibyte' option (see section AE.2 Initial Options), or set the environment variable EMACS_UNIBYTE. You can also customize enable-multibyte-characters or, equivalently, directly set the variable default-enable-multibyte-characters to nil in your init file to have basically the same effect as `--unibyte'.

To convert a unibyte session to a multibyte session, set default-enable-multibyte-characters to t. Buffers which were created in the unibyte session before you turn on multibyte support will stay unibyte. You can turn on multibyte support in a specific buffer by invoking the command toggle-enable-multibyte-characters in that buffer.

With `--unibyte', multibyte strings are not created during initialization from the values of environment variables, `/etc/passwd' entries etc. that contain non-ASCII 8-bit characters.

Emacs normally loads Lisp files as multibyte, regardless of whether you used `--unibyte'. This includes the Emacs initialization file, `.emacs', and the initialization files of Emacs packages such as Gnus. However, you can specify unibyte loading for a particular Lisp file, by putting `-*-unibyte: t;-*-' in a comment on the first line. Then that file is always loaded as unibyte text, even if you did not start Emacs with `--unibyte'. The motivation for these conventions is that it is more reliable to always load any particular Lisp file in the same way. However, you can load a Lisp file as unibyte, on any one occasion, by typing C-x RET c raw-text RET immediately before loading it.

The mode line indicates whether multibyte character support is enabled in the current buffer. If it is, there are two or more characters (most often two dashes) before the colon near the beginning of the mode line. When multibyte characters are not enabled, just one dash precedes the colon.