Explain that a handler handles by default this specific controller and all it's child controllers - all controllers that were called from it. <iframe width="560" height="315" src="https://www.youtube.com/embed/k5btpJgXglw?list=PL1DEQjXG2xnIGbO3DlvFQjv-T0OXM81r-" frameborder="0" allowfullscreen></iframe>