checkboxes, radio buttons and $_POST['<name>']

Hi HELP!!! I have read through the manual about using $_POST['<name>'] to retrieve data from forms, but what happens when a form element is not filled in or checked? If I have a checkbox on a form called "chk1" I get an error from PHP when I try this: $chk1 = $_POST['chk1']; // error if user did not chech the checkbox on the form!!! How do ya usefully retrieve the fact that a form element has not been filled in/checked? Be Well, John-Erik Omland ==================================== "Rhythm is the basis of life,

    not steady forward progress.

The forces of creation, destruction, and preservation

         have a whirling, dynamic interaction."
                                        - Kabbalah