code: private void performClearOperation(ModelElementInstanceImpl modelElement, Collection<DomElement> elementsToRemove) {
      Collection<ModelElementInstance> modelElements = ModelUtil.getModelElementCollection(elementsToRemove, modelElement.getModelInstance());
      for (ModelElementInstance element : modelElements) {
        modelElement.removeChildElement(element);
      }
    }
docs: the "clear" operation used by this collection