Mojo.Event.listenForFocusChanges(node, handler)

This function can be used to listen for changes in which element has focus inside the specified node.

A listener object is returned which implements a stopListening() method. This can be called tp permanently cancel the listener, removing its event listeners.

Parameter	Type	Description
node		Node on which to listen for events
handler	Function	Function called when focus changes. Passes the newly focused element or null.

Example usage:

        this.controller.setupWidget('emailAddress', this.emailAttributes, this.emailModel);
                
        $('emailAddress').observe(Mojo.Event.propertyChange, this.emailChanged.bind(this));
        this.emailFocusHandler = this.emailHandler.bind(this);
        Mojo.Event.listenForFocusChanges($('emailAddress'), this.emailFocusHandler);