This isn't even Adobe's first attempt at solving this problem. Old, old versions of Photoshop in the early 90's (I believe it was introduced in Photoshop 2.5)

This isn't even Adobe's first attempt at solving this problem. Old, old versions of Photoshop in the early 90's (I believe it was introduced in Photoshop 2.5) had an ancient hack called "quick edit" which would allow you to select a file and then open a "slice" of the file, which is a specified bounding box within the file (and not only x,y coordinates -- it could also select a subset of the color channels). It would then present that chunk of the file as its own standalone document window which you could manipulate to your heart's content, then when you saved it, it wrote the slice back out to the original document. It only supported a subset of graphics formats because each one had to have custom code to read and write the slice data.