Listing 1

left_pane.left = 0;
left_pane.width = { 
if ( parent.sizing == "sizing_percentage") 
  then parent.width * left_size;
  else left_size;
}
in_between.left = left_pane.width;
// the space between the panes
in_between.width = 10 ;
right_pane.left = in_between.left + in_between.width;
right_pane.width = parent.width - left_pane.width - in_between.width;