These would be place-able like windows.
The arrowloops would allow a hearthling to fire arrows through only the wider end. Enemies would not be able to fire back through unless directly next to it, so placing them a little ways up the wall would stop them from being able to shoot back.
The murderholes and machicolations would be place-able on any block (wall, floor, slab, etc.) allowing hearthings to fire arrows through them, but only downwards. The hearthling would have to stand on top of them to fire through, and enemies would not be able to fire back through unless really close underneath.
The reason for these is because using regular windows allows enemies to easily fire back. To counter these, movable mantlets would be used by the enemy goblins or other players’ soldiers in multiplayer. These would require additional coding, but that code could also be used for other movable things, like carts.