Return value of selected radio button using Prototype

gistfile1.js

/**
 * 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
 *
 * From: http://xavisys.com/using-prototype-javascript-to-get-the-value-of-a-radio-group/
 */
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;
}