I am already using those attributes to change the collapsed and expanded icons. But what I want is to change the plus(+) and minus(-) marks to my own icons. Is there a way for me to do this.
I found one solution. I don't know whether this is the best way. I did it by overriding the style classes .rf-trn-hnd-exp and .rf-trn-hnd-colps .
background:url('/example/resources/img/plus.jpg') no-repeat center;
background:url('/example/resources/img/minus.jpg') no-repeat center;