hi,
i think there is no html-attribute to do so. but you could write a simple javascript-function. something like this would probably work:
function doSelect(itemNo) {
if (document.myForm.mySelection.options[itemNo].selected == true) {
document.myForm.mySelection.options[itemNo].selected = false;
} else {
document.myForm.mySelection.options[itemNo].selected = true; }
}
you have to call this function everytime the user clicks on an option.
i'm not sure, whether the code above runs. maybe you have to fix it a little bit
regards
christoph