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In one instance in NWN:EE this has a valid use case the engine recognises: Additional "Spellbook" columns in spells.2da, which are now referenced by column name in classes.2da.
Referencing Columns
When a column for a 2da references another 2da, and the entry requires an ID to use from the other 2da (eg feats.2da having a column to link to a line in spells.2da), the ID you must give it is actually the line number offset from base (base being where index 0 starts). This basically just means 2da line ID numbers cannot be skipped, but is mostly only relevant where a persistent server has heavily modified 2da's.
2DA List
This is a list of the different core 2da files (we're ignoring tileset specific ones but there will be a generic entry for them, plus the multitude of class and package 2das) with a note about the usage for client or server, and line limits (if known). Anything in this list is used by the game, the unused ones are listed later on this page.
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