Marks an achievement for tracking in the WatchFrame.
- Number - ID of the achievement to add to tracking.
- A maximum of WATCHFRAME_MAXACHIEVEMENTS (10 as of 5.4.8) tracked achievements can be displayed by the WatchFrame at a time.
- You may need to manually updated the AchievementUI and WatchFrame after calling this function.
- Patch 3.1.0 / API (2009-04-14): Renamed from SetTrackedAchievement to AddTrackedAchievement.
- Patch 3.0.2 / API (2008-10-14): Added.