https://github.com/rathena/rathena/blob/master/doc/script_commands.txt#L2778
EQI_COMPOUND_ON (-1) - Item slot that calls this script (In context of item script) - exclusive to getequipid
EQI_ACC_L (0) - Accessory 1
EQI_ACC_R (1) - Accessory 2
EQI_SHOES (2) - Footgear (shoes, boots)
EQI_GARMENT (3) - Garment (mufflers, hoods, manteaux)
EQI_HEAD_LOW (4) - Lower Headgear (beards, some masks)
EQI_HEAD_MID (5) - Middle Headgear (masks, glasses)
EQI_HEAD_TOP (6) - Upper Headgear
EQI_ARMOR (7) - Armor (jackets, robes)
EQI_HAND_L (8) - Left hand (weapons, shields)
EQI_HAND_R (9) - Right hand (weapons)
EQI_COSTUME_HEAD_TOP (10) - Upper Costume Headgear
EQI_COSTUME_HEAD_MID (11) - Middle Costume Headgear
EQI_COSTUME_HEAD_LOW (12) - Lower Costume Headgear
EQI_COSTUME_GARMENT (13) - Costume Garment
EQI_AMMO (14) - Arrow/Ammunition
EQI_SHADOW_ARMOR (15) - Shadow Armor
EQI_SHADOW_WEAPON (16) - Shadow Weapon
EQI_SHADOW_SHIELD (17) - Shadow Shield
EQI_SHADOW_SHOES (18) - Shadow Shoes
EQI_SHADOW_ACC_R (19) - Shadow Accessory 2
EQI_SHADOW_ACC_L (20) - Shadow Accessory 1