Custom Form Elements

The examples only show how to 'check all' elements. How can I use a link to check a single checkbox element.

One way to do so, is to set the property checked to true (="checked") and fire a change event:

var el = $("idOfCheckbox");

el.checked = true;
el.fireEvent("change");

another way could be to retrieve the instance of cfe from the original checkbox and call the check method

$("idOfCheckbox").retrieve("cfe").check()

Think of Custom Form Elements as a decolayer on top of the standard functionality of form elements, you may use the standard DOM methods or cfe methods either way