What are all of the possible tags for PGN? In a PGN file, there are tags like:

[Event "Tournament"]
[White "John Smith"]


And so on. I would like to know all the possible tags for PGN files so I can use them in a PGN file that my friend is demanding for.
PGN standards are described here. There are seven more-or-less required tags:

[Event]
[Site]
[Date]
[Round]
[White]
[Black]
[Result]


and many different supplemental tags, for example [WhiteElo] and [BlackElo] for the players' ratings, [Board] for the board number in team events, and [TimeControl] for information about the time-control used.