CASP is one of The Sims 4's packed file types. There is one for every CAS item (counting each color as its own item), and contains such info as the item's gender, age group, outfit category, ect.
More information about CASP can be found here: https://github.com/Sims4Group/Sims4Tools/wiki/0x034AEECB
Below is the CASP data for ymShoes_AnkleWork_Brown as an example.
Version: 0x0000001A TGIoffset: 0x00000115 PresetCount: 0x00000000 Name: ymShoes_AnkleWork_Brown SortPriority: 5.0000 SecondarySortIndex: 0x0005 PropertyID: 0x00001DAE AuralMaterialHash: 0x95CC8017 ParmFlags: 0x2C (AllowForRandom, ShowInUI, ShowInCASDemo) ExcludePartFlags: 0x0000000000000000 ExcludeModifierRegionFlags: 0x00000000 --- FlagList: CASFlagList (0xE) --- --- CASFlagList[0] --- FlagCatagory: 0x0044 (AgeAppropriate) FlagValue: 0x0054 --- CASFlagList[1] --- FlagCatagory: 0x0044 (AgeAppropriate) FlagValue: 0x0048 --- CASFlagList[2] --- FlagCatagory: 0x0044 (AgeAppropriate) FlagValue: 0x0123 --- CASFlagList[3] --- FlagCatagory: 0x0044 (AgeAppropriate) FlagValue: 0x0047 --- CASFlagList[4] --- FlagCatagory: 0x0041 (Color) FlagValue: 0x005B --- CASFlagList[5] --- FlagCatagory: 0x004C (ColorPalette) FlagValue: 0x0118 --- CASFlagList[6] --- FlagCatagory: 0x004C (ColorPalette) FlagValue: 0x011B --- CASFlagList[7] --- FlagCatagory: 0x004C (ColorPalette) FlagValue: 0x011F --- CASFlagList[8] --- FlagCatagory: 0x0060 (Fabric) FlagValue: 0x0213 --- CASFlagList[9] --- FlagCatagory: 0x0046 (OutfitCategory) FlagValue: 0x004D --- CASFlagList[A] --- FlagCatagory: 0x0054 (Shoes) FlagValue: 0x0180 --- CASFlagList[B] --- FlagCatagory: 0x0042 (Style) FlagValue: 0x03D9 --- CASFlagList[C] --- FlagCatagory: 0x0042 (Style) FlagValue: 0x00F0 --- CASFlagList[D] --- FlagCatagory: 0x005B (Uniform) FlagValue: 0x0265 --- SimlolencePrice: 0x00000000 PartTitleKey: 0x00000000 PartDesptionKey: 0x00000000 UniqueTextureSpace: 0x00 BodyType: 0x00000008 Unused1: 0x00000008 AgeGender: 0x00001078 Unused2: 0x01 Unused3: 0x00 --- SwatchColorList: SwatchColorCode (0x1) --- [0]: ff98654b --- BuffResKey: 0x00 (0x00000000-0x00000000-0x0000000000000000) VarientThumbnailKey: 0x00 (0x00000000-0x00000000-0x0000000000000000) NakedKey: 0x00 (0x00000000-0x00000000-0x0000000000000000) ParentKey: 0x00 (0x00000000-0x00000000-0x0000000000000000) SortLayer: 0x000029CC --- LODBlockList: LodBlockList (0x4) --- --- LodBlockList[0] --- Level: 0x01 --- LODAssetList: LodAssetList (0x1) --- --- LodAssetList[0] --- CastShadow: 0x00008000 Sorting: 0x00000000 SpecLevel: 0x00002000 --- --- ByteIndexList: LODKeyList (0x1) --- [0]: 0x01 (0x015A1849-0x00E8506E-0x91F13B832B1BB9BA) --- Unused: 0x00000008 --- LodBlockList[1] --- Level: 0x02 --- LODAssetList: LodAssetList (0x1) --- --- LodAssetList[0] --- CastShadow: 0x00008000 Sorting: 0x00000000 SpecLevel: 0x00002000 --- --- ByteIndexList: LODKeyList (0x1) --- [0]: 0x02 (0x015A1849-0x00E8506D-0x91F13B832B1BB9BA) --- Unused: 0x0000001F --- LodBlockList[2] --- Level: 0x03 --- LODAssetList: LodAssetList (0x1) --- --- LodAssetList[0] --- CastShadow: 0x00008000 Sorting: 0x00000000 SpecLevel: 0x00002000 --- --- ByteIndexList: LODKeyList (0x1) --- [0]: 0x03 (0x015A1849-0x00E8506C-0x91F13B832B1BB9BA) --- Unused: 0x0000001F --- LodBlockList[3] --- Level: 0x00 --- LODAssetList: LodAssetList (0x1) --- --- LodAssetList[0] --- CastShadow: 0x00008000 Sorting: 0x00000000 SpecLevel: 0x00002000 --- --- ByteIndexList: LODKeyList (0x1) --- [0]: 0x04 (0x015A1849-0x00E8506F-0x91F13B832B1BB9BA) --- Unused: 0x00000008 --- --- SimpleList`1: SlotKey (0x2) --- [0]: 0x00 [1]: 0x00 --- DifussShadowKey: 0x05 (0x3453CF95-0x00000000-0xA94CDE01CC27CD17) ShadowKey: 0x06 (0x3453CF95-0x00000000-0x5421774ECD635B18) CompositionMethod: 0x00 (0x00000000-0x00000000-0x0000000000000000) RegionMapKey: 0x07 (0xAC16FBEC-0x00000000-0x91F13B832B1BB9BA) Overrides: 0x00 (0x00000000-0x00000000-0x0000000000000000) NormalMapKey: 0x00 (0x00000000-0x00000000-0x0000000000000000) SpecularMapKey: 0x08 (0xBA856C78-0x00000000-0xF79C8C72F0951ED0) --- CountedTGIBlockList: TGIList (0x9) --- [0]: 0x00000000-0x00000000-0x0000000000000000 [1]: 0x015A1849-0x00E8506E-0x91F13B832B1BB9BA [2]: 0x015A1849-0x00E8506D-0x91F13B832B1BB9BA [3]: 0x015A1849-0x00E8506C-0x91F13B832B1BB9BA [4]: 0x015A1849-0x00E8506F-0x91F13B832B1BB9BA [5]: 0x3453CF95-0x00000000-0xA94CDE01CC27CD17 [6]: 0x3453CF95-0x00000000-0x5421774ECD635B18 [7]: 0xAC16FBEC-0x00000000-0x91F13B832B1BB9BA [8]: 0xBA856C78-0x00000000-0xF79C8C72F0951ED0 ---
CASP files can be extracted from ClientFullBuild0.package, and used to create default replacements. For example, you could extract the CASP file above, for ymShoes_AnkleWork_Brown, and change "AgeGender: 0x00001078" to "AgeGender: 0x00003078", thereby making the shoes appear for both males and females. Of course, the meshes for male and female bodies are different, so this would look weird in-game, but it will work easily for things like makeup, eyebrows, and anything for children, as their meshes are identical.
AgeGender[]
Gender[]
0x00001000 = male
0x00002000 = female
0x00003000 = both genders
Age[]
0x00000001 = baby
0x00000002 = toddler
0x00000004 = child
0x00000008 = teen
0x00000010 = young adult
0x00000020 = adult
0x00000030 = young adult + adult
0x00000040 = elder
0x00000060 = adult + elder
0x00000070 = young adult + adult + elder
0x00000078 = teen + young adult + adult + elder
0x0000007F = all ages
Note: Thank you to CmarNYC for this info http://modthesims.info/showthread.php?p=4547734#post4547734