code: function(x, y) {
          if ( (x == null) || (y == null) ) {
              throw new TypeError('Bounds.add cannot receive null values');
          }
          return new OpenLayers.Bounds(this.left + x, this.bottom + y,
                                       this.right + x, this.top + y);
      }
docs: APIMethod: add
  Shifts the coordinates of the bound by the given horizontal and vertical
  deltas.
  
  (start code)
  var bounds = new OpenLayers.Bounds(0, 0, 10, 10);
  bounds.toString();
  // => "0,0,10,10"
  
  bounds.add(-1.5, 4).toString();
  // => "-1.5,4,8.5,14"
  (end)
  
  This method will throw a TypeError if it is passed null as an argument.
  
  Parameters:
  x - {Float} horizontal delta
  y - {Float} vertical delta
  
  Returns:
  {<OpenLayers.Bounds>} A new bounds whose coordinates are the same as
  this, but shifted by the passed-in x and y values.