What is the namespace that is used for WPF?

x:ClassName xmlns:custom="clr-namespace:SDKSample;assembly=SDKSampleLibrary" and Page x:Class="WPFApplication1.MainPage" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:custom="clr-namespace:SDKSample;assembly=SDKSampleLibrary">