Summary of Identifiers

identifier:
    nondigit
    identifier nondigit
    identifier digit

nondigit: one of
    _ a b c d e f g h i j k l mn o p q r s t u v w x y z
    A B C D E F G H I J K L MN O P Q R S T U V W X Y Z

digit: one of
    0 1 2 3 4 5 6 7 8 9

See also

Lexical Grammar