docs: function(evt) {
          var passes = true;
          if (this.pixelTolerance != null && this.down && this.down.xy) {
              passes = this.pixelTolerance >= this.down.xy.distanceTo(evt.xy);
              // for touch environments, we also enforce that all touches
              // start and end within the given tolerance to be considered a click
              if (passes && this.touch && 
                  this.down.touches.length === this.last.touches.length) {
                  // the touchend event doesn't come with touches, so we check
                  // down and last
                  for (var i=0, ii=this.down.touches.length; i<ii; ++i) {
                      if (this.getTouchDistance(
                              this.down.touches[i], 
                              this.last.touches[i]
                          ) > this.pixelTolerance) {
                          passes = false;
                          break;
                      }
                  }
              }
          }
          return passes;
      }