code: function(key, value, expiration) {
  
              // set item
              var ret = this._storage.setItem(key, value);
  
              // set expiration timestamp (only if defined)
              if (expiration) {
                  this.updateExpiration(key, expiration);
              }
  
              // return set value return value
              return ret;
          }
docs: Set item.
  @param key: Item key to set (string).
  @param value: Value to store (string).
  @param expiration: Expiration time, in seconds. If not provided, will not set expiration time.
  @param return: Storage.setItem() return code.