The method that Revit will invoke to get an HTML formatted description of the server. 
   Namespace:   Autodesk.Revit.DB.Mechanical  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2014 
Syntax
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Return Value
The HTML format description of the server.Remarks
 The HTML description is used by Revit unless it is empty or the server is not available, in which case, Revit will use the plain text description from IExternalServer.GetDescription().