This method must be called within the lambda passed to QueuedTask.Run.
Remarks
This method was created so developers have a way to uniquely assign a value or multiple values to an element that can not be changed in the UI and therefore provides a predictable way to find an element. Each entry has a key/value pair and you find the value using the GetCustomProperty method. You can overwrite values simply be reentering the same key with a different value. There are no methods to remove keys.