1) We search logins on the current page only when entered login length is less 4 chars. I.e. when we enter @use we still search only on the current page between html elements with class user and login (e.g. <span class="user login man">paul</span>).

6.11.3+: In case the collection can have assignees (≤20), we also immediately match the usernames of potential assignees. If ≥21 potential assignees and an assignee hasn’t been mentioned on the page yet, they are not matched locally and they can only be matches through case 2 below.

2) But when we enter @user(login length >= 4 chars) we call AJAX/REST_API request to users/autocomplete endpoint. There we search ALL users which logins are started with entered string like user*. The results are sorted by following priority:

1. if user_login == entered string like user,
2. users which can be assignee of the collection,
3. users which are members of the collection,
4. all other users.