Radio Button List Client Side Validation

[ricio2000]

Does anybody know how to implement client side validation on the text of the selected radio button in a RadioButtonList server control. What needs to occur is that a dropdown list control will be selected. The text is will be something like "RuleX". I will the need to grab the string "RuleX" associated with the selected radio button and see if it contains this string as a substring. If it doesn't I will display an alert message to the user. My question is how would I go about grabbing that string for the selected radiobutton in the radiobuttonlist server control.

Any help will be appreciated.