3 Lexical and syntactic conventions

As m4 reads its input, it separates it into tokens. A token is either a name, a quoted string, or any single character, that is not a part of either a name or a string. Input to m4 can also contain comments. GNU m4 does not yet understand multibyte locales; all operations are byte-oriented rather than character-oriented (although if your locale uses a single byte encoding, such as ISO-8859-1, you will not notice a difference). However, m4 is eight-bit clean, so you can use non-ASCII characters in quoted strings (see Changequote), comments (see Changecom), and macro names (see Indir), with the exception of the NUL character (the zero byte ‘'\0'’).