The source of an information transition between panels.
The information transition starts when a panel is closed and the information is visually transferred to another panel, like when dismissing by swipe or pressing an accept button. For example, an incoming call notification may transition to a main process panel showing the call progress.
The transition does not transfer the data but rather an intent. The destination panel obtains its information by other means.
A class reference of the type of panel that the information transitions from.