@requiem The enter=send thing isn't modern anymore due to the more complex chats.
UX is normally like this (Facebook, Google Hangouts, Slack, Atlassian-products just to name a few):
- Type @
- Type a letter
- Get a list of matching items (for example users)
The first entry in this list is automatically selected. As you type the list gets narrowed down accordingly (cause the search pattern gets longer). Again, always the first item in this list is selected.
If you hit enter your character sequence gets auto-completed with the selected entry from the list.