Because its Auto Layout rules resist clipping (these rules are called compression resistance), the window cannot resize any further. The only way to allow it to shrink beyond this size is to demote or remove one or both of its “do not clip” subview rules. A similar rule, called content hugging, allows a view to resist padding and stretching, keeping the frame of each view close to the natural size of the content it presents.
Terms: compression resistance; content hugging
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