Usage of some notification strings

There are several strings that starts with “notifications.alt”.
They are used for the “alt” attribute for notification item.
Is it used for screen readers only? If so, how is it spoken?
Because some English strings doesn’t end by “by/from”, as I assumed it’s spoken “Edit your post by someone nameOfTopic”

Use:
https://github.com/discourse/discourse/blob/master/app/assets/javascripts/discourse/widgets/notification-item.js.es6#L98