كيف أقوم بتعيين الامتدادات المسموح بها لحقل النموذج المُدار؟

$form['picture']['file'] = array(
  '#type' => 'managed_file',
  '#title' => t('picture'),
  '#description' => t('Allowed extensions: gif png jpg jpeg'),
  '#default_value' => (isset($foo->picture->fid) ? $foo->picture->fid : ''),
  '#upload_location' => variable_get('picture_upload_location'),
  '#upload_validators' => array(
    'file_validate_extensions' => array('gif png jpg jpeg'),
    // Pass the maximum file size in bytes
    'file_validate_size' => array(MAX_FILE_SIZE*1024*1024),
  ),
);