# File rbSnack/tkSnackUtil.rb, line 506
   def getYfor( *indxs )
     raise "unitialized world frame" if @worldFrame.type!=Array or @worldFrame[3]==nil or @worldFrame[1]==nil
     rtv = *indxs.collect{ |i|  screenY2World @boxes[i][1]}
     rtv=rtv[0] if rtv.length==1
     rtv
   end