Custom UI Skins/Look'n'Feel in GM13? | Questions about GWEN.

I was looking through the Gmod13 change list, and i noticed
“Now uses GWEN skins”

What does this mean?

Does Derma now render with GWEN’s theme? Or is the in-game ui actually rendered with GWEN?

Will it be possible to use custom derma skins? like this

It is possible to change the GWEN skin, but i’ve only ever done it manually. What I did was, to copy over the contents of the file that defined the default GWEN skin, and change the file address from the default gwen skin png ( or what ever you want to call it ) to a skin I’ve designed myself.

What about things like SetSkin though?

Say if i were to make an addon, and i wanted it’s ui to have a custom theme/skin.
Would this still be possible?

It uses GWEN’s png skin system

Will that be customizable?

It’s obvious that you can’t edit an image, so why ask!!!11!!&1

Can someone explain to me how to export a gwen file?