code: function(x1, y1, x2, y2) {
          if (arguments.length === 1) y1 = x2 = y2 = x1;
          this._bx1 = x1;
          this._bx2 = x2;
          this._by1 = y1;
          this._by2 = y2;
          this.trigger("BoundaryOffset");
          this._calculateMBR();
          return this;
      }
docs: @
  #.offsetBoundary
  @comp 2D
  @kind Method
  
  Extends the MBR of the entity by a specified amount.
  
  @trigger BoundaryOffset - when the MBR offset changes
  @sign public this .offsetBoundary(Number dx1, Number dy1, Number dx2, Number dy2)
  @param dx1 - Extends the MBR to the left by this amount
  @param dy1 - Extends the MBR upward by this amount
  @param dx2 - Extends the MBR to the right by this amount
  @param dy2 - Extends the MBR downward by this amount
  
  @sign public this .offsetBoundary(Number offset)
  @param offset - Extend the MBR in all directions by this amount
  
  You would most likely use this function to ensure that custom canvas rendering beyond the extent of the entity's normal bounds is not clipped.