Mentions (often known as @mentions) are a useful way of drawing someone's attention to a page or comment.
When you mention a user, they'll receive a notification by email.
The following users can being mentioned:
Participants of a ticket which are only Jira Servicedesk portal customers cannot being mentioned, unless they have left a comment in the ticket, then they will become a commenter on the ticket.
To mention someone using autocomplete, type '@' in the editor then start typing their name. Choose the person you want to mention from the list of suggestions.
Jira/Confluence will suggest people you've mentioned previously (after yourself, of course).
It then continues to suggest matches as you type. If you've not mentioned the person recently, we'll also include information about whether they've commented or contributed to the current page, to help you find the right person, fast.
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https://confluence.atlassian.com/doc/mentions-251725350.html