var pathfilename=@"c:\some\file.txt";
System.Diagnostics.Process.Start($"explorer", $"/select,\"{pathfilename}\"");
<UserControl x:Name="userControl" x:Class="Myns.Myctl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:Myns"
d:DataContext="{d:DesignInstance Type=local:MyItem, IsDesignTimeCreatable=True}">
</UserControl>
to insert special ascii char like newline ( 0xa : 10 ) put hex value into HH as follow:
&#xHH;
<TextBlock Text="sample
NEWLINE"/>