The default number of changes stored in the stack is 1000, but you could change it through the Depth property of the History:
.ImageEditorUI.ImageEditor.History.Depth = 500;
The items in the history are not accessible and the only thing that comes to mind in order to obtain them is to subscribe to the CommandExecuted event and implement a custom logic to store the records.
For more details about this feature
you could check the History article
in our documentation.
Hope this is helpful.
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