I'm unsure what the "Exotic item" category is used for. The description on the "Resources" page suggests expensive items. However, this conflicts with the actual selection of items: Glitterworld medicine, Elephant tusk, Genepack are not what you would call expensive. Meanwhile, items such as telescopes are not included. Others still have the exotic type but not the category (ex:textbook).
I'm guessing "Items with the ExoticMisc tradetag or uncraftable non-materials non-TechHediff sold by exotic traders" is the intended target. However, this also has some issues: From the ExoticMisc tradetag angle: - Gliterworld medicine belongs both here and to medicine, while other mixed cases are superseded by this category (mech serum has a thingCategories of drug but this is ignored, for instance). - Luciferium is not included. - Neither rocket launcher (doomsday nor triple) is included. - The "orbital bombardment targeter", "orbital power beam targeter", "tornado generator" are excluded. - Craftable items with the ExoticMisc tradetag (ex:control pack, bandwidth pack from biotech) are excluded (The 2nd criterion at work, I guess). - Anomaly items are missing, that may be a work in progress. (Tome would a candidate under both cut offs)
From the "uncraftable non-materials non-TechHediff sold by exotic traders" angle: - Artifacts can be sold by exotic traders, but none is included. - Some items that may belong here don't (Polux seed, Deathrest capacity serum)
So, I ask: What is the deciding factor?