Public Shared Function IsRelationshipPartUri ( _
    partUri As Uri _
) As Boolean

Dim partUri As Uri
Dim returnValue As Boolean

returnValue = PackUriHelper.IsRelationshipPartUri(partUri)

public static bool IsRelationshipPartUri(
    Uri partUri
)

public:
static bool IsRelationshipPartUri(
    Uri^ partUri
)

public static function IsRelationshipPartUri(
    partUri : Uri
) : boolean

You cannot use methods in XAML.