How to prevent the highlighting of InlineUIContainer on mouse click?

Question

Consider the following FlowDocument inside a WPF RichTextBox:

<RichTextBox Width="150" FontSize="30">
  <FlowDocument>
    <Paragraph>
      <Run Text="abc"/>
      <InlineUIContainer>
        <Border BorderBrush="Black" BorderThickness="1" CornerRadius="4" Width="30" Height="20"/>
      </InlineUIContainer>
      <Run Text="def"/>
    </Paragraph>
  </FlowDocument>
</RichTextBox>

When I click on the Border it becomes highlighted in blue:

How can I prevent that? I would like it to position the caret instead, like this:

I have already tried the following properties without success:

• IsHitTestVisible = false
• IsEnabled = false
• IsManipulationEnabled = false
• Focusable = false
• IsFocused = false

Answer 1

use this xaml:

 <RichTextBox x:Name="rchText" Width="150" FontSize="30">
      <FlowDocument MouseDown="rch_MouseDown">
         <Paragraph>
              <Run Text="abc"/>
              <InlineUIContainer>
             <Border x:Name="brdText" BorderBrush="Black" BorderThickness="1" CornerRadius="4" Width="30" Height="20"/>
             </InlineUIContainer>
             <Run Text="def"/>
        </Paragraph>
     </FlowDocument>
</RichTextBox>

then:

private void rch_MouseDown(object sender, MouseButtonEventArgs e)
{
   var mousePoint = Mouse.GetPosition(rchText);
   var borderPos = brdText.TranslatePoint(new Point(0, 0), rchText);
   if(mousePoint.X > borderPos.X && mousePoint.X < (borderPos.X + brdText.ActualWidth) && mousePoint.Y > borderPos.Y && mousePoint.Y < (borderPos.Y + brdText.ActualWidth))
   {
     e.Handled = true;
   }
}