public bool IsPending { get; }

Public ReadOnly Property IsPending As Boolean
	Get

public:
property bool IsPending {
	bool get ();
}

When an event is requested to raise it is not executed immediately; instead, it waits for the next possible opportunity, which is determined by various internal conditions in Revit (policy similar to invoking external commands). When the opportunity comes, the event is executed by calling the event's handler. In the meantime, the event is 'Pending'.