Scroll bars stand in an uncomfortable place with one foot on the WM side and the other in the application. The user wants to be able to control the size, scale,

Scroll bars stand in an uncomfortable place with one foot on the WM side and the other in the application. The user wants to be able to control the size, scale, and position of the window without asking permission from the app. (And who was the evil programmer who gave web sites the ability to disable zooming? But I digress.) But an app that's at the mercy of the operating system for drawing its scroll bars is going to lose usability if it wants to provide infinite scrolling, or simulate a slide-show with vertical position. In those cases it would be better to let the app control the appearance of the scroll bars. Which is to say, the regular window scroll bar that we're familiar with is being overloaded for two different purposes: to interact with the app and to interact with the WM. Perhaps we should have two scroll bars to avoid this confusion?