Unable to edit textblock content in WPF

I am working on my first WPF application, and I notice that I cannot edit text values ​​in any of my text blocks.

I can’t find anything bad here that would prevent me from changing it ...

<Label Content="Line Terminator" Grid.Row="0" Grid.Column="0" Margin="5"></Label>
<Border BorderThickness="1" BorderBrush="LightBlue" Grid.Row="0" Grid.Column="1" Margin="5">
    <TextBlock x:Name="txtLineTerm" Focusable="True" IsManipulationEnabled="True" Padding="3"></TextBlock>
</Border>
<Label Content="Field Terminator" Grid.Row="0" Grid.Column="2" Margin="5"></Label>
<Border BorderThickness="1" BorderBrush="LightBlue" Grid.Row="0" Grid.Column="3" Margin="5">
    <TextBlock x:Name="txtFieldTerm" Focusable="True" IsManipulationEnabled="True" Padding="3"></TextBlock>
</Border>

Can anyone see the problem? I feel that there is a concept that I am missing here. Any explanation would be greatly appreciated.