<Grid  xmlns:local="clr-namespace:MyProject"
       xmlns:mylib="clr-namespace:MyLibraryNamespace;assembly=MyLibrary">

  <!-- MyProject.MyLocalType in local assembly -->
  <local:MyLocalType /> 

  <!-- MyLibraryNamespace.MyLibraryType in MyLibrary assembly -->
  <mylib:MyLibraryType />
</Grid>

