Source (The ListBox)
The object that raised the event. This is a property you will
generally be interested in. It’s useful to note that with routed
events this is likely to be different from the sender.
OriginalSource (The ScrollViewer)
This returns original reporting source. That is the object that
really raised the event. This property does not change as the
event travels along its route.
Sender (The Grid)
Sender is where we captured the event.
A bool that lets you know if the event has already been handled.
You should mark this true in your own handlers.
This identifies the type of event that was raised. Many events
have the same signature, and a single handler might be
responsible for several events.