Before reading this description, please brush up on your chemistry knowledge (Don't fear, it's short and painless)
Periodic Table adds order to many items and spells in WoW. These are organized into sets. Like most Ace addons it's focus is efficiency. PT is a LibStub library for managing these sets (ex: Misc.Spell.Mount, Consumable.Food.Edible.Cheese, Misc.Minipet, ClassSpell) for other addons.
If you are looking for an Ace'd alternative to ReagentInfo (the tooltip display) check out Mendeleev by MoonWolf, which you can find on Curse or WoWI.
Item sets are stored as a comma-delimited strings and parsed out into a table only if requested. This speeds up load time and ensures that memory is only used for sets that are actively used.
If you are interested in using PT with your mod feel free to read the source code (there's not a lot). The comments will tell you everything you need to know.
PeriodicTable's "modules" are simply sets of sets. Particular mods can link the exact sets they need.
© 2008-2009 Curse Inc.