public static function &processors()
    {
        if (!self::$processors) {
            // Add default processors.
            self::$processors = [
                new MergeIntoOpenApi(),
                new MergeIntoComponents(),
                new ImportTraits(),
                new AugmentSchemas(),
                new AugmentProperties(),
                new BuildPaths(),
                // new HandleReferences(),

                new InheritProperties(),
                new AugmentOperations(),
                new AugmentParameters(),
                new MergeJsonContent(),
                new MergeXmlContent(),
                new OperationId(),
                new CleanUnmerged(),
            ];
        }

        return self::$processors;
    }