Drag and drop files into collection

I want an image collection.
I'll also want a collection containing files.

When I'm in a collection, I'd like to be able to simply drag the file (image or other) from outside (a file on my computer, an image from a website, etc.) and drop it into the collection.

Initially in the “Collection” mini-app (the only way to view collections right now, I think?), and in the inline versions when they become available.