JQuery form validation - validate form based on other form field

Question

hey guys,

I"m using Jquery form validation which in the basic form looks like this

$('#shopping_form').validate({          
  submitHandler: function(){
  $.post("/url", { message: messageval}, function(data) {
  ......
  ......
  },
}
,rules: {
    message: { required:true },
    price: { number: true  }                
}
});

Now I am adding two radio buttons to this form call them radio1 and radio2. If radio1 is selected then the field message is required and for radio2 its not a required field.

How can I add this kind of rule. Thanks for your help in advance