Isn&#x27;t that somewhat possible with extensions and constraints? At least that was the impression given by last year&#x27;s WWDC talk [1], unless you&#x27;re thinking of something else?<p>[1]: <a href="https:&#x2F;&#x2F;developer.apple.com&#x2F;videos&#x2F;play&#x2F;wwdc2015&#x2F;408&#x2F;" rel="nofollow">https:&#x2F;&#x2F;developer.apple.com&#x2F;videos&#x2F;play&#x2F;wwdc2015&#x2F;408&#x2F;</a>