Rule Value() {
        return FirstOf(
                Keyword(),
                Literal(),
                Function(),
                VariableReference(),
                URL(),
                Font(),
                AlphaFilter(),
                ExpressionFunction(),
                FilterFunction()
        );
    }
Rule Value ( ) { return FirstOf ( Keyword ( ) , Literal ( ) , Function ( ) , VariableReference ( ) , URL ( ) , Font ( ) , AlphaFilter ( ) , ExpressionFunction ( ) , FilterFunction ( ) ) ; }
Any token used as a value in an expression
Future: Accessors