An interface that supports addition of external applications to Revit. 
   Namespace:   Autodesk.Revit.UI  
  Assembly:   RevitAPIUI  (in RevitAPIUI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
| C# | 
|---|
   |  
| Visual Basic | 
|---|
   |  
| Visual C++ | 
|---|
   |  
Remarks
 External applications are permitted to customize the Revit UI, and to add events and updaters to the session.