@AlexDS study carefully the .blend file on tutorial homepage. Bones are the target for offset modifier - as they move, uvs move to new coordinates with different part of texture, in this case with eyes or mouth drawn different way.
@harrisyu it’s probably not easier to animate with setting keyframe numbers - first it assumes special texture format - grids and rows. As it’s done now you can of course use grids and rows layout but it’s only special case. I like to have all of character’s textures in one place and different parts of body take different amount of space so they don’t fit to this layout. Second, you’ll probably agree that animating with graphicall symbols is easier than with setting numbers. With numbers you have to remember that 3 stands for eyes closed and 4 for left eye open…
And creating helper object for grid row layout is trivial (it’s always trivial).
@eXKR it’s written in C and addons are in Python (correct me if I’m wrong). I think it should stay in C because of performance reasons.
For what purposes do you need to scale or rotate uvs?
Tutorial is ready but if there will be voices it’s too brief I’ll add some screenshots with info.