code: func FindExtensions(tx ReadTx, by By) ([]*api.Extension, error) {
  	checkType := func(by By) error {
  		switch by.(type) {
  		case byIDPrefix, byName, byCustom, byCustomPrefix:
  			return nil
  		default:
  			return ErrInvalidFindBy
  		}
  	}
  
  	extensionList := []*api.Extension{}
  	appendResult := func(o api.StoreObject) {
  		extensionList = append(extensionList, o.(extensionEntry).Extension)
  	}
  
  	err := tx.find(tableExtension, by, checkType, appendResult)
  	return extensionList, err
  }
docs: // FindExtensions selects a set of extensions and returns them.