An element which allows an API applications to organize and store data. 
   Namespace:   Autodesk.Revit.DB.ExtensibleStorage  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2013 
Syntax
Remarks
 Applications can create instances of these elements to logically organize different sets of ExtensibleStorage entities into separate elements. This allows an application to update one set of data in a local workshared project without locking other elements.