The following are tables with two cells. The first cell contains two buttons and a separator between them. The second cell has a   and its width is set to "100%", so it forces the first one to shrink as much as it can.
  as separator (using nowrap) (bug on Opera):
   

Space as separator (using nowrap):
 

  as separator (without nowrap) (bug on Firefox):
   

Space as separator (without nowrap):