src/main/java/com/bazaarvoice/jless/parser/Parser.java
Rule AlphaFilter() {
        return Sequence(
                Sequence(
                        "alpha(", Ws0(),
                        "opacity", Ws0(),
                        '=', Ws0(),
                        Digit1(), Ws0(),
                        ')'
                ),
                push(new SimpleNode(match()))
        );
    }
Rule AlphaFilter() {
        return Sequence(
                Sequence(
                        "alpha(", Ws0(),
                        "opacity", Ws0(),
                        '=', Ws0(),
                        Digit1(), Ws0(),
                        ')'
                ),
                push(new SimpleNode(match()))
        );
    }
'alpha(' Ws0 'opacity' Ws0 '=' Ws0 Digit1 Ws0 ')'