set preferred e-mail address

[mcnesium]

The database table oc_cards_properties has a field preferred, but it is unclear to me, what it is used for?
There is no setting in the frontend that can select a preferred address.

MariaDB [nextcloud]> describe oc_cards_properties;
+---------------+---------------------+------+-----+---------+----------------+
| Field         | Type                | Null | Key | Default | Extra          |
+---------------+---------------------+------+-----+---------+----------------+
| id            | bigint(20) unsigned | NO   | PRI | NULL    | auto_increment |
| addressbookid | bigint(20)          | NO   | MUL | 0       |                |
| cardid        | bigint(20) unsigned | NO   | MUL | 0       |                |
| name          | varchar(64)         | YES  | MUL | NULL    |                |
| value         | varchar(255)        | YES  | MUL | NULL    |                |
| preferred     | int(11)             | NO   |     | 1       |                |
+---------------+---------------------+------+-----+---------+----------------+

Most contact entries have a 0, but very few rather old entries have a 1 there. Was there a setting in earlier versions?

If there are multiple mail addresses per contact card, it would be awesome to be able to set a preferred address over the others.