Aim: Add placeholder within comment for instance...
"Hi, why is this ticket not done / updated for more than X days?"
We want to personalize this comments like

"HI $current_assignee, this ticket has not been updated since $last_updated_time please explain what's the reason."

So we need to use placeholders in the Comments that will be replace by JIRA.

"Hi Daniel Roß, this ticket has not been updated since 01. January 2014 please explain what's the reason."

This concept only works with the text formatting notation of username where users are are still required to manually select from a list.