code: function _add_to(stack, item_or_list){
  
  	var ret = [];
  	
  	if( tcache[stack] ){
  	    if( item_or_list ){
  		if( ! us.isArray(item_or_list) ){ // ensure listy
  		    item_or_list = [item_or_list];
  		}
   		ret = tcache[stack].concat(item_or_list);
  	    }else{
  		ret = tcache[stack].concat();
  	    }
  	}
  
  	return ret;
      }
docs: Push an item or a list onto a list, returning the new list. This is a copy--no shared structure.