A dispenser or dropper which is facing the world border or outside the world border can be activated. This means that it can for example spawn entities outside the world border or place blocks such as water, lava or powder snow.
MC-140127 you are able to glitch through the worldborder using a boat and a dispenser
MC-113426 Hoppers can push items in containers outside the world border
MC-227722 Redstone components outside the world border are read/updated by blocks inside the world border