Objectives
Objectives are hints that are displayed on the client, They show the player what he has to complete in order to win the game. They are optional, it's perfectly ok to not show any objectives and let the player figure out himself what to do.
Currently only WorldObjects can be objectives. If a WorldObject is marked as objective (the boss which has to be killed), its health bar is dislpayed in the objective list on the client (top right corner). This way the boss is always visible to all players, even if the player doesn't have the boss in its target (useful for healer roles, which usually have one of their team members targetted).
Newly created objectives are marked as not cleared. Meaning they have not yet been completed. Once the objective is completed, you can mark it as cleared. The client will display cleared objectives with a green-ish color.
Once an objective is cleared, it can not be un-cleared again. But you can remove objectives, if you want to guide the players through multiple consecutive objectives.