How does orientation work, and what is shouldRotateToOrientation?

[Dmitry Blotsky]

Hey folks,

I’ve had a bug forwarded my way where a Cordova app wouldn’t switch orientation 
on iOS unless the following code was present:

function onDeviceReady() {
    ...
    window.shouldRotateToOrientation = function (degrees) {
        return true;
    }
    ...
};

Could someone please explain why it is needed? Is this in one of our plugins? 
And perhaps also: what else/instead is needed to have a Cordova app properly 
support flipping of screen orientation?

Kindly,
Dmitry