I use the SplitView control in UWP and want to increase the width of the SplitView if the user clicks on certain top-level items in it. The SplitView should display a second level of options. Microsoft's UWP Mail App does something like this: if you click on "Folders", you get a list of all available folders as an extension to the SplitView. This extension is nicely animated.
I can easily increase the SplitView's OpenPaneLength with a setter like this: