I explored a few options - the reason I decided to make it controlled by the user was so it didn't have to open in a new window (as you can only control the width of the window with JS in a separate window).
Thanks for the feedback though - might create a separate self-running version at some point.
This only works when resizing the window? Would an ever-increasing div work? If you floated it right the size would always increase on the left, mimicking the drag and resize action that the user is doing.
That said, I get that you're pushing the limits as it is here and you've likely already considered this as an option.
Thanks for the feedback though - might create a separate self-running version at some point.