ViewTargetActionSupport#append()

Appends the view's element to the document body. If the view does not have an HTML representation yet the element will be generated automatically.

If your application uses the rootElement property, you must append the view within that element. Rendering views outside of the rootElement is not supported.

Note that this method just schedules the view to be appended; the DOM element will not be appended to the document body until all bindings have finished synchronizing.