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27.2 Enabling Multibyte Characters

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

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, we call that unibyte mode. 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 in unibyte mode 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.

To edit a particular file in unibyte representation, visit it using find-file-literally. See section 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 Specifying a Coding System for File Text. 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 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 (see section Local Variables in Files). 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) near the beginning of the mode line, before the indication of the visited file's end-of-line convention (colon, backslash, etc.). When multibyte characters are not enabled, nothing precedes the colon except a single dash. See section The Mode Line, for more details about this.


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