Border style based on standard control causing runtime error - wpf

Question

I created a new WPF project by Blend 2017 (.net 4.7) with one window and this Xaml (added no code behind):
<Window x:Class="WpfApp1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
mc:Ignorable="d"
Title="MainWindow"
Height="350"
Width="525">
<Window.Resources>
<Style x:Key="_borderStyleWithChildBinding"
TargetType="{x:Type Border}"
BasedOn="{StaticResource {x:Type Border}}">
<Setter Property="BorderBrush"
Value="{Binding RelativeSource={RelativeSource Self}, Path=Child.Fill}" />
</Style>
</Window.Resources>
<Grid Width="50"
Height="30"
Margin="10">
<Border BorderThickness="5"
Style="{StaticResource _borderStyleWithChildBinding}">
<Border.Child>
<Rectangle Width="20"
Height="10"
Fill="Green" />
</Border.Child>
</Border>
</Grid>
</Window>
It compiles but reports a runtime error concerning line
BasedOn="{StaticResource {x:Type Border}}"
Exception: System.Windows.Markup.XamlParseException: A value for System.Windows.Markup.StaticResourceHolder caused an exception.
InnerException: Resource System.Windows.Controls.Border cannot be found.
The designer is smart enough to show the right thing:

Answer 1

We can solve the problem by omitting the x:Key and the BasedOn property of the border style:
<Window x:Class="WpfApp1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
mc:Ignorable="d"
Title="MainWindow"
Height="350"
Width="525">
<Window.Resources>
<Style TargetType="{x:Type Border}" >
<Setter Property="BorderBrush"
Value="{Binding RelativeSource={RelativeSource Self}, Path=Child.Fill}" />
</Style>
</Window.Resources>
<Grid Width="50"
Height="30"
Margin="10">
<Border BorderThickness="5">
<Border.Child>
<Rectangle Width="20"
Height="10"
Fill="Green" />
</Border.Child>
</Border>
</Grid>
</Window>