protected function getExtendedDefaultSchemaObject(array $objectSchema)
    {
        if (!(is_array($objectSchema['extends_default']) && 2 == count($objectSchema['extends_default']))) {
            throw new SchemaParserException('The "extends_default" directive should be an array with exactly 2 values.');
        }
        $folder = $this->schemaFolder;
        $this->schemaFolder = $this->defaultSchemaFolder;

        $this->parseAll(reset($objectSchema['extends_default']));
        $parent = $this->getObjectFromSchema(
            $this->schemas[$this->defaultSchemaFolder][$objectSchema['extends_default'][0]],
            $objectSchema['extends_default'][1]
        );

        $this->schemaFolder = $folder;

        return $parent;
    }