function classUpdateChecked($tag, $el, options) {
        // setTimeout() introduced by #357
        setTimeout(function () {
            var c = "checked",
                isChecked = $el.is(":" + c);

            if(!$el.attr("readonly")) {
                if ($el.prop) {
                    // jQuery 1.6+
                    $el.prop(c, isChecked);
                } else {
                    // jQuery 1.5 and below
                    if (isChecked) {
                        $el.attr(c, c);
                    } else {
                        $el.removeAttr(c);
                    }
                }
            }
            
            classUpdate($tag, options.checkedClass, isChecked);
        }, 1);
    }
Updating the "checked" property can be a little tricky.  This
changed in jQuery 1.6 and now we can pass booleans to .prop().
Prior to that, one either adds an attribute ("checked=checked") or
removes the attribute.

@param {jQuery} $tag Our Uniform span/div
@param {jQuery} $el Original form element
@param {Object} options Uniform options for this element