code: function(ch, w) {
     if(!ch || ch.length == 0) return Number.MAX_VALUE;
     var areaSum = 0, maxArea = 0, minArea = Number.MAX_VALUE;
     for(var i=0, l=ch.length; i<l; i++) {
       var area = ch[i]._area;
       areaSum += area; 
       minArea = minArea < area? minArea : area;
       maxArea = maxArea > area? maxArea : area; 
     }
     var sqw = w * w, sqAreaSum = areaSum * areaSum;
     return Math.max(sqw * maxArea / sqAreaSum,
             sqAreaSum / (sqw * minArea));
   }
docs: /*
  Method: worstAspectRatio
  
  Calculates the worst aspect ratio of a group of rectangles.
  
  See also:
  
  <http://en.wikipedia.org/wiki/Aspect_ratio>
  
  Parameters:
  
  ch - An array of nodes.
  w  - The fixed dimension where rectangles are being laid out.
  
  Returns:
  
  The worst aspect ratio.