http://schemas.microsoft.com/winfx/2006/xaml/presentation uses a concept called
Mapping CLR Namespaces to XML Namespaces in an Assembly
What this by adding
http:// you can refer more than one assembly in as single namespace variable.
e.g. x:Name,x:Type here x may be referring more than one assembly or to hide which assembly it points.
By any arbitrary string value means there is no format for naming the namespace it can be any string.
