Viewbox is a pretty handy 'container' in WPF.. It is a decorator that scales its child content to the size available to the viewbox ( if child is smaller it scales it up >1, if child is bigger it scales it down such that it fits based on some stretch direction).
You can find source code for a sample viewbox here.
If you want to see a ugly (yet still useful for those knowing viewbox) harness, there is a sample here..
Sorry for no docs; the control itself is straight forward. Please check the docs for WPF viewbox to see how to use it; the SL2 version above mimics WPF.
Please do review the source if you are using it for a real project.