Minecraft wiki entry for JSON_format, associated text:  conditions:
 location: The location at the center of the block the item was used on.
Tags common to all locations[show]
 item: The item used on the block.
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]