Minecraft wiki entry for Block_entity_format, associated text: : The block entity's root tag.
 name: The jigsaw block's name. This jigsaw block will be aligned with another structure's jigsaw block which has this value in the target tag.
 target: The jigsaw block's target name. This jigsaw block will be aligned with another structure's jigsaw block which has this value in the name tag.
 target_pool: The jigsaw block's target pool to select a structure from.
 final_state: The block that this jigsaw block becomes.
 joint: The joint option value, either "rollable" or "aligned".