Found It!  You need to download the

[Visual Studio 2013 SDK][sdk]
=====

Once installed, the project template will appear here:

![demo][demo]

[sdk]: http://www.microsoft.com/en-us/download/details.aspx?id=40758
[demo]: http://i.imgur.com/M6dBU0H.png

Both of these articles talk about how to develop extensions for VS2013, but both presume that you have an extension project type available

* [Extending the Visual Studio Environment][extending]
* [Creating Extensions By Using the VSIX Project Template][vsix]

As of 11/9/13, there are already [544 extensions][gallery] for VS2013 in the gallery, so I'm guessing it's possible, but I can't find the template anywhere.

[extending]: http://msdn.microsoft.com/en-us/library/vstudio/esk3eey8.aspx
[vsix]: http://msdn.microsoft.com/en-us/library/vstudio/dd885241.aspx
[gallery]: http://visualstudiogallery.msdn.microsoft.com/site/search?f%5B0%5D.Type=VisualStudioVersion&f%5B0%5D.Value=12.0&f%5B0%5D.Text=Visual%20Studio%202013

Where is Visual Studio 2013 Extensibility VSIX Project Template

There used to be really great designer support for Windows 8.0 apps in Visual Studio 2012.  In the [Device Panel][Device Panel], you could move to different `VisualStates` within the `VisualStateManager.VisualStateGroups` on your page and it would update the appropriate properties at design time. 

In 8.1, the `VisualState`s are [no longer based on specific snapped layouts][responsive], but you can still use the `VisualStateManager` and update based on the screen `width`.

*Q*: How can I get these changes to update at design time?

-----


Here's a simple example of a change that works at runtime, but not design time.

**MainView.xaml.vb**:



    Private Sub MainView_Loaded(sender As Object, e As RoutedEventArgs) Handles Me.Loaded
        AddHandler Me.SizeChanged, AddressOf WindowSizeChanged
        ApplyViewState(Me.Width, Me.Height)
    End Sub

    Private Sub WindowSizeChanged(sender As Object, e As SizeChangedEventArgs)
        ApplyViewState(e.NewSize.Width, e.NewSize.Height)
    End Sub

    Private Sub ApplyViewState(ByVal viewWidth As Double, ByVal viewHeight As Double)
        If viewWidth < 350 Then
            VisualStateManager.GoToState(Me, "SmallLayout", True)
        Else
            VisualStateManager.GoToState(Me, "RegularLayout", True)
        End If
    End Sub

**MainView.xaml**:



    <Page x:Name="PageRoot"
        x:Class="WinStoreMvvmTemplate.View.MainView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
        
        <Grid Background="Red" x:Name="ContentGrid">
            
            <VisualStateManager.VisualStateGroups>
                <VisualStateGroup>
                    <VisualState x:Name="RegularLayout"/>
                    <VisualState x:Name="SmallLayout">
                        <Storyboard>
                            <ObjectAnimationUsingKeyFrames 
                                Storyboard.TargetName="ContentGrid"
                                Storyboard.TargetProperty="Background">
                                <DiscreteObjectKeyFrame KeyTime="0" Value="Blue"/>
                            </ObjectAnimationUsingKeyFrames>
                        </Storyboard>
                    </VisualState>
                </VisualStateGroup>
            </VisualStateManager.VisualStateGroups>
    
        </Grid>
    </Page>


-----

Here's a view at **Design Time**: *(incorrect)*

![design][design]

Here's a view at **Run Time**: *(correct)*

![runtime][runtime]

[Device Panel]: http://msdn.microsoft.com/en-us/library/windows/apps/jj129464.aspx

[responsive]: http://blogs.windows.com/windows/b/appbuilder/archive/2013/07/02/build-talk-of-the-week-beautiful-apps-at-any-size-on-any-screen.aspx
[design]: http://i.imgur.com/hdZdAf7.png
[runtime]: http://i.imgur.com/XEpMUvr.png