code: function findOctantsByLevel(octant, level, depth, result) {
  
  	const children = octant.children;
  
  	let i, l;
  
  	if(depth === level) {
  
  		result.push(octant);
  
  	} else if(children !== null) {
  
  		++depth;
  
  		for(i = 0, l = children.length; i < l; ++i) {
  
  			findOctantsByLevel(children[i], level, depth, result);
  
  		}
  
  	}
  
  }
docs: Recursively fetches all octants with the specified depth level.
  
  @private
  @param {Octant} octant - An octant.
  @param {Number} level - The target depth level.
  @param {Number} depth - The current depth level.
  @param {Octant[]} result - A list to be filled with the identified octants.