Assume there is a graphically intensive visual feature in app X. It includes dimming out some part of the screen at some point in the program. The story revolves around implementing a similar feature in our app which is of the same genre.
The PO insists at adding an acceptance criterion, "achieve the same exact effect as in the reference app".
Is that a valid acceptance criterion?
How can we know that we have achieved it in terms of the definition of done?