Minecraft wiki entry for Enchanting, associated text:  Enchantments: Contains enchantments on this item that affect the way the item works.
: A single enchantment.
 id: The name of the enchantment.
 lvl: The level of the enchantment, where 1 is level 1. Values are clamped between 0 and 255 when reading.
 StoredEnchantments: Contains enchantments for enchanted books.
: A stored enchantment, identical structure to each enchantment in Enchantments.
 RepairCost: Number of experience levels to add to the base level cost when repairing, combining, or renaming this item with an Anvil.