Namespaces

A XAML file usually declares a default XAML namespace in its root element. This default namespace defines elements that can be declared without qualifying them by a prefix (e.g. x:). XAML namespaces apply only to the specific element on which they are declared and its children, which explains why they are typically placed on the root element. ^ref

Most XAML files have two xmlns declarations

• xmlns maps a default XAML namespace

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml

x

xmlns:x maps a separate XAML namespace for XAML-defined language elements to the x: prefix:

• x:Name uniquely identified object elements for access to the object from code-behind :point_right: x:Name attribute
• x:Key sets a unique key for each resource in a ResourceDictionary 👉 x:Key attribute
• x:Class specifies the CLR namespace and class name for the class that provides code-behind for a XAML page. The x:Class directive configures XAML markup compilation to join partial classes between markup and code-behind. In this example it can be seen how it refers to the MainPage class within the Project namespace. 👉 x:Class directive

Language elements are commonly used features necessary for Windows Runtime apps. For example, to join any code-behind to a XAML file through a partial class, you must name that class as the x:Class attribute in the root element of the XAML file.

// C#  
namespace Project
{
  public sealed partial class MainPage : Page
  {
    public MainPage()
    {
      this.InitializeComponent();
    }
    ...
  }
}

<!-- XAML -->
<Page
  x:Class="Project.MainPage"
  ...>
...
</Page>

mc

mc: indicates and supports a markup compatibility mode for reading XAML.

xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"