code: function(model) {
  
      const modelPrev = model.collection.prev(model);
      const modelNext = model.collection.next(model);
      let mPrevSel, mNextSel;
      if ((typeof modelPrev !== "undefined" && modelPrev !== null)) { mPrevSel = this._getSelection(modelPrev); }
      if ((typeof modelNext !== "undefined" && modelNext !== null)) { mNextSel = this._getSelection(modelNext); }
      return [mPrevSel,mNextSel];
    }
docs: looks at the selection of the prev and next el TODO: this is very naive, as there might be gaps above or below