How do I tag a user on my Post?

I would like to know how do I tag a user to my post and what are the restrictions.

Just below the post there is an option to Tag Users. You need type the username and select the correct one. That would tag the user.

Restrictions:

1. Newbies cannot tag users.

2. Some users may have restricted the tagging feature to Buddies only or completely Off from the settings. So you cannot tag those users.

3. You can only tag maximum 5 people in one post.

4. Once you have tagged someone you cannot add or update the list. Since we do not want this to be misused.