WPF Has Accumulated Multiple WPF XML Namespaces over Time It’s practically a given that real-world WPF XAML will choose to use the WPF XML namespace as the default namespace, but it turns out that more than one XML namespace is mapped to the main WPF types in the various System.Windows namespaces. WPF 3.0 shipped with support for http://schemas.microsoft.com/winfx/2006/xaml/presentation, but WPF 3.5 defined a new XML namespace— http://schemas.microsoft.com/netfx/2007/xaml/presentation—mapped to the same WPF types. (WinFX was the original name for a set of technologies introduced in the .NET Framework 3.0, including WPF,WCF, and WF. That term was abandoned, hence the change in namespace.) WPF 4 has once again defined a new XML namespace that is mapped to the same WPF types:http://schemas.microsoft.com/netfx/2009/xaml/presentation.Despite all these options, it is best to stick with the original http://schemas.microsoft.com/winfx/2006/xaml/presentation namespace because it works in all versions of WPF.(Whether your content works with all versions of WPF is another story, as to do so it must stick to features present only in WPF 3.0.) Note that Silverlight also supports the http://schemas.microsoft.com/winfx/2006/xaml/presentation namespace to make it easier to use XAML meant for WPF inside a Silverlight project, although it also defines its own alternative namespace, http://schemas.microsoft.com/client/2007, which is not supported by WPF. The XML namespaces are confusing. They are not schemas. They do not represent a closed set of types that were available when the namespace was introduced. Instead, each version of WPF retrofits all previous namespaces with any new assembly/namespace pairs introduced in the new version. Therefore, the winfx/2006 namespace effectively means “version 3.0 or later,” the netfx/2007 namespace means “version 3.5 or later,” and so on. However,WPF 4 accidentally excludes some namespace/assembly pairs from the netfx/2009 namespace,which makes using omitted types (like TextOptions) pretty challenging! When loose XAML is loaded into Internet Explorer, it is loaded by PresentationHost.exe, which decides which version of the .NET Framework to load based on the XML namespaces on the root element. If the netfx/2009 namespace is present it will load version 4.0, otherwise it will load whichever 3.x version is present.
at Page.28
