code: function() {
  
          var xy = getXY(this.getEl()),
              t  = this.thumb;
  
          if (!this.thumbCenterPoint || !this.thumbCenterPoint.x) {
              this.setThumbCenterPoint();
          }
  
          if (xy) {
  
              this.logger.log("newPos: " + xy);
  
              if (xy[0] != this.baselinePos[0] || xy[1] != this.baselinePos[1]) {
                  this.logger.log("background moved, resetting constraints");
  
                  // Reset background
                  this.setInitPosition();
                  this.baselinePos = xy;
  
                  // Reset thumb
                  t.initPageX = this.initPageX + t.startOffset[0];
                  t.initPageY = this.initPageY + t.startOffset[1];
                  t.deltaSetXY = null;
                  this.resetThumbConstraints();
  
                  return false;
              }
          }
  
          return true;
      }
docs: Checks the background position element position.  If it has moved from the
  baseline position, the constraints for the thumb are reset
  @method verifyOffset
  @return {boolean} True if the offset is the same as the baseline.