Holds a set of members that are defined in markup, which apply to the x:Class of the parent element.
In the .NET Framework XAML Services implementation, there is no backing class or underlying member implementation for x:Members. x:Members is a special XAML member that can exist as a member on any type. In a XAML node stream, x:Members is represented as a member named Members, from the XAML language XAML namespace. The member Members contains a read-only generic list of Member objects. In typical markup the individual members are specified as x:Property property elements. x:Property is a more precise type specifically for properties of types and is assignable to x:Member. For more information, see x:Property Directive.
To support a practical usage of x:Members as a means to specify member definitions in markup, the members must be associated with a class that can be modified. The intended model is that x:Members exists as a member of a type that specifies an x:Class. However, the mechanism for associating types and members or for producing dynamic member definitions is not supported at the .NET Framework XAML Services level. This is left to individual frameworks that have application models that support member definitions from XAML. Typically, MSBUILD build actions that markup-compile the XAML and either integrate it with code-behind or produce pure from-XAML assemblies are needed to support that feature.
x:Members for Windows Workflow Foundation
For Windows Workflow Foundation, x:Members contains the members of a custom activity composed entirely in XAML, or XAML –defined dynamic members for an activity designer with code-behind. x:Class must also be specified on the root element of the XAML production. This is not a requirement at the .NET Framework XAML Services level, but becomes a requirement when the XAML production is loaded by the MSBUILD build actions that support custom activities and Windows Workflow Foundation XAML in general. x:Members must be the first child element in markup of the object element that declares the x:Class.