API IsInInstance

Checks whether the player is in an instance and the type of instance. inInstance, instanceType = IsInInstance

Returns

 * inInstance : Flag - Whether the player is in an instance; nil otherwise.
 * instanceType : String - The instance type:
 * "none" when outside an instance
 * "pvp" when in a battleground
 * "arena" when in an arena
 * "party" when in a 5-man instance
 * "raid" when in a raid instance

Details
This functon returns correct results immediately upon PLAYER_ENTERING_WORLD.