RepeaterCanvas.subscribeContextFocusChanged Method
        
 Subscribe a handler for the context focus changed event.
 
         
        Parameters
        
            - callback
            
 
            - 
                
Type: function (event, eventType)
The event handler. 
            - unsubscribe
            
 
            - 
                
Type: Boolean - May be null
(Optional) true to unsubscribe, false to subscribe 
            - once
            
 
            - 
                
Type: Boolean - May be null
(Optional) True to register handler as a single use handler.