When that creature is killed, a list of potential sets will be generated, then iterate through them to roll for drops. Insignificant sets like crafting materials are rolled individually, for as many sets as applicable, so it's possible to find multiple kinds of materials from a single kill.
Drop rates for armor and weapons are hardcoded and are kept as a separate category of drops with their own rates.
|CreatureDefID||Integer. Corresponds to CreatureDef ID|
|Explicit||Boolean. Obsolete and mostly left at zero. If set to true, this disables level-based sets for that creature (level-based sets are defined in Packages.txt) and instead only use sets listed in this table entry.|
|PackageList||String. A list of sets (but also accepts package names), separated by commas. When selecting drops, package names are resolved into a list of sets. Typically this field normally lists sets. Refer to Sets.txt for set definitions.|
|Name||Not loaded or used by the server. Just serves as documentation info within the file.|