Minecraft wiki entry for World_border, associated text: There are no hitboxes in the world border.
Due to a bug in coordinate system, liquids can be placed outside the border, but they do not flow.
Mobs and items float outside the border.
Dying from border damage results in the death message: "[Player] suffocated in a wall"
Blocks can be placed on both sides of the world border.
Eroded badlands biome, found at the edge of the world. Check the image for seed and cords.