e', token(lexer.WHITESPACE, ...))
    lex:add_rule('keyword', token(lexer.KEYWORD, ...))
    lex:add_rule('identifier', token(lexer.IDENTIFIER, ...))
    lex:add_rule('string', token(lexer.STRING, ...))
    lex:add_rule('comment', token(lexer.COMMENT, ...))
    lex:add_rule('number', token(lexer.NUMBER, ...))
    lex:add_rule('label', token(lexer.LABEL, ...))
    lex:add_rule('operator', token(lexer.OPERATOR, ...))
    </code></pre>

    <p>Note how identifiers come after keywords. In Lua, as with most prog