Some of these pages are no longer intentionally left blank.

One thing we neglected to mention in the release notes is that you can now load up roots other than Window and Grid in the August CTP. The list I believe is anything deriving from Panel, Page, UserControl and ContentControl. 

So if you have the latest installed - try replacing your window1.xaml with this:

<

Button x:Class="WindowsApplication65.Window1"
xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
Height="75" Width="100">
Hello world!
</Button>

If you want to drag and drop into it, replace the contents with a Grid. For button you may have to size the grid in code, as the button layout sizes grid to zero.

More interestingly, you can now design user controls.

<

UserControl x:Class="WindowsApplication65.Window1"
xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
Height="75" Width="100">
<Grid>
</Grid>
</UserControl>

Have fun!