code: @OverrideOnDemand
    protected void onInsertAtIndex (@Nonnegative final int nIndex, @Nonnull final AbstractMicroNode aChildNode)
    {
      throw new MicroException ("Cannot insert children in class " + getClass ().getName ());
    }
docs: Callback that is invoked once a child is to be inserted at the specified
  index.
  
  @param nIndex
  The index where the node should be inserted.
  @param aChildNode
  The new child node to be inserted.