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For objects placed into the game world there are two formids: the reference formid or '''RefID''' (associated with that particular placed object), and the base formid or '''BaseID''' (used for all versions of that same object).
The BaseID provides the information that is common to all instances of that object. For example, every copy of the book ''[[Oblivion:On Oblivion|On Oblivion]]'' has the same BaseID (<code>0002457E</code>); that BaseID record contains information such as the weight, value, appearance, and text of the book. The specific type of record used for the BaseID depends upon the type of item. For example [[
Tes4Mod:Mod File Format/BOOK|BOOK]], [[ Tes4Mod:Mod File Format/WEAP|WEAP]], [[ Tes4Mod:Mod File Format/ NPC_|NPC_]], and [[ Tes4Mod:Mod File Format/CREA|CREA]] are all records used exclusively for BaseIDs. In the Construction Set, all of the formids listed in the "Object Window" are BaseIDs. Most formids provided on this site are BaseIDs.
The RefID provides access to information such as the object's location. There are only three types of records used for RefIDs; the specific type of record depends upon the object:
* For NPCs, a [[
Tes4Mod:Mod File Format/ACHR|ACHR]] record is used.
* For creatures, a [[
Tes4Mod:Mod File Format/ACRE|ACRE]] record is used.
* For all items, a [[
Tes4Mod:Mod File Format/REFR|REFR]] record is used.
In game, when you console-click on a placed object, the formid that you will see is the RefID, not the BaseID. In the CS, when you look at objects in the "Cell View", the IDs are all RefIDs; if you edit the object, the BaseID is provided under "Base Object" (and "Edit Base" allows you to edit it). When RefIDs are provided on this site, they are explicitly identified as RefIDs.
Formids were introduced for several reasons, but a main reason was to do away with the mod conflicts that plagued the Morrowind community -- mods conflict has been removed by almost completely isolating mods from each other.
Unfortunately, this isolation makes it difficult to intentionally make mods interact with each other. In fact, using CS by itself, it's impossible to make an esp directly reference (use) anything in any other esp! Fortunately, several tricks have been developed to deal with this. For more info, see [[
Tes4Mod:Mod Integration|Mod Integration]].
===Multiple Mods in CS4===
Note that CS4 ''does'' allow you to load non-master mods, but it ''does not'' allow your mod to become dependent on them. Again, see [[
Tes4Mod:Mod Integration|Mod Integration]] for more info. Despite this, the modindex of the formids belonging to your mod will not be '01', but rather will reflect the load position of your mod -- which is always last. E.g., if you load Oblivion plus 4 esps, then the modindex that you'll see in the formids for your data objects will be '04' (since your mod would be fifth in order and the order numbering starts at '00').
While you might suspect that this would cause problems if your mod is loaded later into CS4 without those other esps, or when it's loaded into the game, CS4 and the game engine seem to adjust for it. (However, any changes that you made to non-esm mods may raise errors.)
=== Formid Fixup ===
For details on exactly how to load and merge multiple mods see the [[
Tes4Mod: FormID_Fixup|FormID Fixup]] page.