Control only on one platform - XAML and OnPlatform

I want to add label (or other element) only on one platform, how achieve that using XAML? I tried:

<OnPlatform x:TypeArguments="View">
  <OnPlatform.WinPhone>
    <Label Text="Only on WinPhone"></Label>
  </OnPlatform.WinPhone>
</OnPlatform>

but it throws exception. I guess I could use visibility and set false on every platform, but one, but maybe there is more elegant way.