code: function _quadRetrievePoint(point, quad) {
      if (quad.level < quad.maxLevel) {
        var index = _quadIndex(point, quad.bounds);
  
        // If node does not exist we return an empty list
        if (quad.nodes[index] !== undefined) {
          return _quadRetrievePoint(point, quad.nodes[index]);
        }
        else {
          return [];
        }
      }
      else {
        return quad.elements;
      }
    }
docs: Recursively retrieve every elements held by the node containing the
  searched point.
  
  @param  {object}  point The searched point (x, y).
  @param  {object}  quad  The searched quad.
  @return {array}         An array of elements contained in the relevant
  node.