Minecraft wiki entry for JSON_format, associated text:  conditions:
 delta: The change in durability (negative numbers are used to indicate a decrease in durability).
 delta:
 max: The maximum value.
 min: The minimum value.
 durability: The remaining durability of the item.
 durability:
 max: The maximum value.
 min: The minimum value.
 item: The item before it was damaged, allows you to check the durability before the item was damaged.
Tags common to all items[show]
 player: The player that would get the advancement. May also be a list of predicates that must pass in order for the trigger to activate.
All possible conditions for entities[show]