Indicates if the propagation of this event has been stopped.
If true, processing of any event listeners in the current node and any
subsequent nodes in the event flow is prevented. This takes effect
immediately, and it affects event listeners in the current node. In
stopsPropagation indicates that it doesn't take effect until
all the event listeners in the current node finish processing.
bool get isImmediatePropagationStopped => _isImmediatePropagationStopped;