code: function tweenProp (start, end, easingFunc, position) {
        return start + (end - start) * easingFunc(position);
      }
docs: /*!
  Tweens a single property.
  @param {number} start The value that the tween started from.
  @param {number} end The value that the tween should end at.
  @param {Function} easingFunc The easing curve to apply to the tween.
  @param {number} position The normalized position (between 0.0 and 1.0) to
  calculate the midpoint of 'start' and 'end' against.
  @return {number} The tweened value.