docs: function intersection( arr1, arr2 ){
  	var rtn = [];
  
  	if ( arr1.length > arr2.length ){
  		let t = arr1;
  
  		arr1 = arr2;
  		arr2 = t;
  	}
  
  	for( let i = 0, c = arr1.length; i < c; i++ ){
  		let d = arr1[i];
  
  		if ( arr2.indexOf(d) !== -1 ){
  			rtn.push( d );
  		}
  	}
  
  	return rtn;
  }