src/main/java/com/bazaarvoice/jless/parser/Parser.java
Rule URL() {
        return Sequence(
                Sequence(
                        "url(", Ws0(),
                        FirstOf(
                                String(),
                                OneOrMore(FirstOf(AnyOf("-_%$/.&=:;#+?"), Alphanumeric()))
                        ), Ws0(),
                        ')'
                ),
                push(new SimpleNode(match()))
        );
    }
Rule URL() {
        return Sequence(
                Sequence(
                        "url(", Ws0(),
                        FirstOf(
                                String(),
                                OneOrMore(FirstOf(AnyOf("-_%$/.&=:;#+?"), Alphanumeric()))
                        ), Ws0(),
                        ')'
                ),
                push(new SimpleNode(match()))
        );
    }
'url(' (String / [-_%$/.&=:;#+?Alphanumeric]+) ')'