Minecraft wiki entry for Block_entity_format, associated text: : The block entity's root tag.
 Progress: How far the block has been moved. Can be 0.0, 0.5, and 1.0.
 LastProgress: Unknown.
 State: Unknown.
 NewState: Unknown.
 Sticky: True if this piston is sticky.
 AttachedBlocks: The list of positions of blocks it should move.
: A block's X position.
: A block's Y position.
: A block's Z position.
: Another block's X position.
: Another block's Y position.
: Another block's Z position.
: etc.
 BreakBlocks: The list of positions of blocks it should break.
: A block's X position.
: A block's Y position.
: A block's Z position.
: Another block's X position.
: Another block's Y position.
: Another block's Z position.
: etc.