Get the ElementIds of Elements that are joined to a mass instance. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2012 
Syntax
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Parameters
- document
-  Type:  Autodesk.Revit.DB Document  
 The Document.
- massInstanceId
-  Type:  Autodesk.Revit.DB ElementId  
 The ElementId of the mass instance.
Return Value
ElementIds of Elements joined to the mass instance.Exceptions
| Exception | Condition | 
|---|---|
| Autodesk.Revit.Exceptions ArgumentException | The ElementId massInstanceId is not a mass instance. | 
| Autodesk.Revit.Exceptions ArgumentNullException | A non-optional argument was NULL |