DepedencyProperty within a MarkupExtension

Question

Is it possible to have a DependencyProperty within a MarkupExtension derived class?

public class GeometryQueryExtension : MarkupExtension
{
    public XmlDataProvider Source { get; set; }

    public string XPath { get; set; }

    public static readonly DependencyProperty ArgumentProperty = DependencyProperty.RegisterAttached(
        "Argument",
        typeof(string),
        typeof(GeometryQueryExtension)); // this wont work because GeometryQueryExtension is not a DependencyProperty

    public string Argument
    {
        get
        {
            return (string)GetValue(ArgumentProperty); // this wont even compile because GeometryQueryExtension doesnt derive from a class which has GetValue
        }
        set
        {
            SetValue(ArgumentProperty,value);// this wont even compile because GeometryQueryExtension doesnt derive from a class which has SetValue
        }
    }
}

The extension is used in the following snippet.

<Label.Content>
    <local:GeometryQueryExtension Source="{StaticResource shapesDS}">
        <local:GeometryQueryExtension.XPath>
            /Shapes/Geometry/{0}
        </local:GeometryQueryExtension.XPath>
        <local:GeometryQueryExtension.Argument>
            <Binding XPath="Geometry"/> <!-- will throw exception when processing this bind -->
        </local:GeometryQueryExtension.Argument>
    </local:GeometryQueryExtension>
</Label.Content>

Is it even possible to build such an extension or am i just barking up the wrong tree ? (the code above wont compile and run, but i posted it here to best illustrate the problem).

Answer 1

No, you can only add dependency properties to classes that are derived from DependencyObject, MarkupExtention is derived directly from Object