code: @Override
      public Shape modelToView(int pos, Shape a, Position.Bias b)
              throws BadLocationException
      {
          if (view != null) { return view.modelToView(pos, a, b); }
          return null;
      }
docs: Provides a mapping from the document model coordinate space to the
  coordinate space of the view mapped to it.
  
  @param pos
  the position to convert
  @param a
  the allocated region to render into
  @return the bounding box of the given position