SetPlayerInSEWorld
Usage
SetPlayerInSEWorld boolean
Where boolean is 0 (not in Shivering Isles) or 1 (in Shivering Isles).
This is a simple function which sets a game engine flag indicating whether the player is in the Shivering Isles or not. It is used extensively by Oblivion.esm to activate/deactivate quests (and thus standard dialog) and is also used by some Oblivion.esm scripts (e.g. on the Grey Cowl).
When to Use
This should be used whenever the player is moved to/from the Shivering Isles realm. In Oblivion.esm it is only used on the door in Niben Bay and the matching door in The Fringe (actually there are three instances of the Shivering Isles side of the door, matching different stages in the SI main quest).
For users mods, it should be used for teleportation spells that take the player to/from Shivering Isles. E.g., a Mark/Recall spell would need to set this as needed.
Note that this is not the only switch that must be set when moving to/from SI -- there are also changes that need to be made to crime and jails. See the scripts attached to the Niben Isle and Shivering Isle portal doors for an example.