code: public static void insertChild( Instance parent, Instance child ) {
  		child.setParent( parent );
  		parent.getChildren().add( child );
  	}
docs: Inserts a child instance.
  <p>
  This method does not check anything.
  In real implementations, such as in the DM, one should
  use {@link #tryToInsertChildInstance(AbstractApplication, Instance, Instance)}.
  </p>
  
  @param child a child instance (not null)
  @param parent a parent instance (not null)