Add a model comments.Mention which inherits from Controllable (Note that he names "Controllable" and "owner" are irritating here, but that is just because these names have historically grown and I currently don't see a name which fits all usages). comments.Mention would have basically only two fields:

owner : GFK to the referred object

comment : FK to the comment which generated the instance, i.e. where the reference is found

Collaborate with MemoParser.parse() to get the list of mentioned objects. Update Mention objects during Comment.after_ui_save()

Add a table comments.MentionsByOwner to be included in the detail of tickets and of users.

Later: Automatically send a notification email "You are mentioned in comment X" when a user is mentioned in a comment.

In CommentsByRFC.column_names we probably want to replace body by body_preview.