code: function () {
      var el;
      if (this.availableEls.length === 0) {
        if (this.data.dynamic === false) {
          warn('Requested entity from empty pool: ' + this.attrName);
          return;
        } else {
          warn('Requested entity from empty pool. This pool is dynamic and will resize ' +
               'automatically. You might want to increase its initial size: ' + this.attrName);
        }
        this.createEntity();
      }
      el = this.availableEls.shift();
      this.usedEls.push(el);
      el.object3D.visible = true;
      return el;
    }
docs: Used to request one of the available entities of the pool.