The following XAML declares the "local" namespace this way:

<Window x:Class="HelloWorld.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:HelloWorld"

mc:Ignorable="d"

FontFamily="./#Aero Matics"

FontSize="36"

Background="#FF124C7A"

Title="NoesisGUI - Hello, World!">

<Image Width="100" Height="100">

<Image.Source>

<local:RenderTargetBitmap/>

</Image.Source>

</Image>