This is documentation for Mathematica 5, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.1)

Documentation / Mathematica / The Mathematica Book / Mathematica Reference Guide / Input Syntax /

A.2.4 Symbol Names and Contexts

Symbol names and contexts.

Symbol names and contexts can contain any characters that are treated by Mathematica as letters or letter-like forms. They can contain digits but cannot start with them.