Minecraft wiki entry for JSON_format, associated text:  conditions:
 block: The block that the player is standing in. Accepts block IDs.
 state: The block states of the block.
 <state_name>: A single block state, with the key name being the state name and the value being the required value of that state.
 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]