code: function _setParticle(position, velocity, phase) {
          if (position !== undefined) {
              //var oldPosition = this._scroll.particle.getPosition1D();
              this._scroll.particleValue = position;
              this._scroll.particle.setPosition1D(position);
              //_log.call(this, 'setParticle.position: ', position, ' (old: ', oldPosition, ', delta: ', position - oldPosition, ', phase: ', phase, ')');
              if (this._scroll.springValue !== undefined) {
                  this._scroll.pe.wake();
              }
          }
          if (velocity !== undefined) {
              var oldVelocity = this._scroll.particle.getVelocity1D();
              if (oldVelocity !== velocity) {
                  this._scroll.particle.setVelocity1D(velocity);
                  //_log.call(this, 'setParticle.velocity: ', velocity, ' (old: ', oldVelocity, ', delta: ', velocity - oldVelocity, ', phase: ', phase, ')');
              }
          }
      }
docs: Updates the scroll offset particle.