expansor WPF vertical

<StackPanel x:Name="RightPanel">
    <Expander x:Name="ExportExpander" ExpandDirection="Right">
        <StackPanel Orientation="Horizontal">
            <TextBlock Name="x" Text="Element One"/> <!--Textblock has Text property-->
            <Button Name="y" Content="Element Two"/>
        </StackPanel>
    </Expander>
</StackPanel>     
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