/**
* Returns the value of the selected radio button in the radio group, null if
* none are selected, and false if the button group doesn't exist
*
* @param {radio Object} or {radio id} el
* OR
* @param {form Object} or {form id} el
* @param {radio group name} radioGroup
*/
function $RF(el, radioGroup) {
    if($(el).type && $(el).type.toLowerCase() == 'radio') {
        var radioGroup = $(el).name;
        var el = $(el).form;
    } else if ($(el).tagName.toLowerCase() != 'form') {
        return false;
    }

    var checked = $(el).getInputs('radio', radioGroup).find(
        function(re) {return re.checked;}
    );
    return (checked) ? $F(checked) : null;
}