How can WPF objects deriving from Freezable be frozen in XAML?

Question

To freeze a Freezable object declared in markup, you use the Freeze attribute defined in XML namespace http://schemas.microsoft.com/winfx/2006/xaml/presentation/options.

In the following example, a SolidColorBrush is declared as a page resource and frozen. It is then used to set the background of a button.

<Page 
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:po="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options" 
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  mc:Ignorable="po">

  <Page.Resources>
    <!-- This brush is frozen -->
    <SolidColorBrush x:Key="MyBrush" po:Freeze="True" Color="Red" />
  </Page.Resources>

  <!-- Use the frozen brush -->
  <Button Background="{StaticResource MyBrush}">Click Me</Button>

</Page>

Source: Freezable Objects Overview

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