I'm trying to create a Markup Extension that will take a string of HTML, convert it to a FlowDocument, and return the FlowDocument. I'm fairly new to creating Markup Extensions and I'm hoping this will be obvious to someone with more experience. Here is my code:

```
[MarkupExtensionReturnType(typeof(FlowDocument))]
public class HtmlToXamlExtension : MarkupExtension
{
    public HtmlToXamlExtension(String source)
    {
        this.Source = source;
    }

    [ConstructorArgument("source")]
    public String Source { get; set; }

    public Type LocalizationResourceType { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        if (this.Source == null)
        {
            throw new InvalidOperationException("Source must be set.");
        }

        FlowDocument flowDocument = new FlowDocument();
        flowDocument.PagePadding = new Thickness(0, 0, 0, 0);
        string xaml = HtmlToXamlConverter.ConvertHtmlToXaml(Source.ToString(), false);

        using (MemoryStream stream = new MemoryStream((new ASCIIEncoding()).GetBytes(xaml)))
        {
            TextRange text = new TextRange(flowDocument.ContentStart, flowDocument.ContentEnd);
            text.Load(stream, DataFormats.Xaml);
        }

        return flowDocument;
    }
}

```

Update: Here is the XAML.

```
<RadioButton.ToolTip>
    <FlowDocumentScrollViewer Document="{ext:HtmlToXaml Source={x:Static res:ExtrudeXaml.RadioButtonCreateBody_TooltipContent}}" ScrollViewer.VerticalScrollBarVisibility="Hidden" />
</RadioButton.ToolTip>

```

And my VS error list:

* Error 3 Unknown property 'Source' for type 'MS.Internal.Markup.MarkupExtensionParser+UnknownMarkupExtension' encountered while parsing a Markup Extension. Line 89 Position 49.
* Error 1 The type "HtmlToXamlExtension" does not include a constructor that has the specified number of arguments.
* Error 2 No constructor for type 'HtmlToXamlExtension' has 0 parameters.