Zend's documentation isn't really clear on this.
The problem is that, by default, Zend automatically renders a view at the end of each controller action. If you're using a layout - and why wouldn't you? - it also renders that. This is fine for normal Web pages, but when you're sending an AJAX response you don't want all that. How do you prevent Zend from auto-rendering on an action-by-action basis?