At the moment, the described behavior is impossible with the API we have in hands. Any descendant of a frame who has AutomaticSize on will result in the expansion of the size no matter what.
Why this is helpful is very specific I’d say, but surely common. I’ve had the need to ignore some instance and not let it expand the size of its parent frame many times.
In this example, the black shadow behind the frame is inserted dynamically so that it’s placed perfectly as if it was parented to the main frame and offsetted by a bit. I am unable to simply parent it to it because as it extends out a little bit more, the main frame who has AutomaticSize set to X will expand which I don’t want. Other solutions to my specific problem would be an identical frame with the same position that has AutomaticSize set to None with the shadow parented to it.
My idea was a property of the descendant that makes it ignored by AutomaticSize.