Designer (deimos) is a component of DesignerPanels and DesignerPanels is a component of Ares. 
Only Ares has a event handler for onError, so if deimos want to call the event handler(in ares.js), DesignerPanels have to regist the onError into events block. 
If there is no define in DesignerPanels, deimos cannot use the Error popup (or define new showErrorPopup function)