Appends an element to the container (possibly creating it first)
If the first parameter is an instance of HTML_QuickForm2_Node then all other parameters are ignored and the method just calls appendChild(). In the other case the element is first created via HTML_QuickForm2_Factory::createElement() and then added via the same method. This is a convenience method to reduce typing and ease porting from HTML_QuickForm.
The default implementation for Containers is to return an array with contained elements' values. The array is indexed the same way $_GET and $_POST arrays would be for these elements.