PluginSetup.xaml

<l:PluginGuiWindow  x:Class="MyPlugin.PluginSetup"
             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" 
             mc:Ignorable="d" 
             Title="MyPlugin Setup"
             xmlns:l="clr-namespace:MLS.HA.DeviceController.Common.Gui;assembly=MLS.HA.DeviceController.Common"
             Height="400" Width="400">
             
             <Label FontSize="15">Add your XAML UI controls to this page.</Label>
</l:PluginGuiWindow>