Something I want to learn... how is it that when you do "Add to Home Screen" with Ello on an iPhone, it creates an icon that behaves much like an "app"... but other web sites don't?

What does Ello do in its mobile interface that signals the iPhone to treat it this way?

I have found a few sites that do this - when you add them, they behave "app"-like. You can switch between them and other apps.

But when I add other websites they just open as new windows inside Safari, without a separate "app"-like experience. (Yes, they have a separate icon, but that launches you into Safari.)

What do Ello and other sites do to get this treatment? Anyone know?

P.S. My testing is on an iPhone 5s running iOS 7.