The return value depends on type. For "attributes", it is the value of the changed attribute before the change. For "characterData", it is the data of the changed node before the change. For "childList", it is null.

public string OldValue { get; }

Public ReadOnly Property OldValue As String
	Get

public:
property String^ OldValue {
	String^ get ();
}

member OldValue : string with get