A symbol is one or more characters chosen from the set of all letters (both upper and lower case), digits and the three characters _.$. On most machines, you can also use $ in symbol names; exceptions are noted in Machine Dependencies. No symbol may begin with a digit. Case is significant. There is no length limit; all characters are significant. Multibyte characters are supported, but note that the setting of the --multibyte-handling option might prevent their use. Symbols are delimited by characters not in that set, or by the beginning of a file (since the source program must end with a newline, the end of a file is not a possible symbol delimiter). See Symbols.
Symbol names may also be enclosed in double quote " characters. In such cases any characters are allowed, except for the NUL character. If a double quote character is to be included in the symbol name it must be preceded by a backslash \ character.