Retinajs, how does it work?

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In the core directory I see there is a retinajs.js file, see https://github.com/concrete5/concrete5/blob/develop/concrete/js/buil...

Does anyone know if it's being used, and if so, where? I see that the file selector attribute outputs a 'data-at2x' attribute, and I wonder at what point images are being swapped.

Ultimately I want to show a bigger preview image in the file picker.

A3020