Adds element ids to the connection. All element ids in an array should be of applicable category. 
   Namespace:   Autodesk.Revit.DB.Structure  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 17.0.0.0 (17.0.1090.0) 
  Since:  2017 
Syntax
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Parameters
- elemIds
 -  Type:  System.Collections.Generic IList   ElementId  
The ElementIdArr containing ids of elements to be added. 
Exceptions
| Exception | Condition | 
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| Autodesk.Revit.Exceptions ArgumentException | One or more element ids was not permitted to be add to the connection. Elements should be of applicable category. -or- One or more element ids was not permitted to be added to the connection. Elements should not be duplicated. | 
| Autodesk.Revit.Exceptions ArgumentNullException | A non-optional argument was NULL |