changed(flags) {
      const f = flags || ALL;
      return f & ADD && this.add.length || f & REM && this.rem.length || f & MOD$1 && this.mod.length;
    }
Indicates if tuples have been added, removed or modified.
@param {number} [flags] - The tuple types (ADD, REM or MOD) to query.
  Defaults to ALL, returning true if any tuple type has changed.
@return {boolean} - Returns true if one or more queried tuple types have
  changed, false otherwise.