src/main/java/com/bazaarvoice/jless/parser/Parser.java
Rule FilterFunction() {
        return Sequence(
                Sequence(
                        "progid:",
                        OneOrMore(FirstOf('.', Ident()))
                ),
                push(new FunctionNode(match())),
                FilterArguments(),
                peek(1).addChild(pop())
        );
    }
Rule FilterFunction() {
        return Sequence(
                Sequence(
                        "progid:",
                        OneOrMore(FirstOf('.', Ident()))
                ),
                push(new FunctionNode(match())),
                FilterArguments(),
                peek(1).addChild(pop())
        );
    }
Ex: progid:DXImageTransform.Microsoft.gradient(startColorstr=@lightColor, endColorstr=@darkColor)