Minecraft wiki entry for Structure_Block, associated text: Custom Data Tag Name
The name of the function to run.
Igloo
"chest" - sets the loot table for a chest beneath the structure block to "chests/igloo_chest" and sets the loot table seed dependent on the world seed.
End city
"Chest" - Sets the loot table for a chest beneath the structure block to "chests/end_city_treasure" and sets the loot table seed dependent on the world seed.
"Sentry" - Creates a shulker at the location of the structure block.
"Elytra" - Creates an item frame entity with an elytra item inside it at the location of the structure block.
Woodland mansion
"ChestSouth" - Sets the loot table for a chest that replaces the structure block to "chests/woodland_mansion" and sets the loot table seed dependent on the world seed.
"ChestNorth" - Sets the loot table for a chest that replaces the structure block to "chests/woodland_mansion" and sets the loot table seed dependent on the world seed.
"ChestEast" - Sets the loot table for a chest that replaces the structure block to "chests/woodland_mansion" and sets the loot table seed dependent on the world seed.
"ChestWest" - Sets the loot table for a chest that replaces the structure block to "chests/woodland_mansion" and sets the loot table seed dependent on the world seed.
"Mage" - Creates an evoker at the location of the structure block.
"Warrior" - Creates a vindicator at the location of the structure block.
Ocean Ruin
"chest" - Creates a chest at the location of the structure block, setting its loot table to either "chests/underwater_ruin_big" or "chests/underwater_ruin_small", with seed dependent on the world seed.
"drowned" - Creates a drowned at the location of the structure block.