The worlds created on the LivingComputers minecraft server have boundaries. One may go from -1024 to 1023 in both directions.
If one gets outside the boundary, one may not move. And if one is far enough outside the boundary, one suffocates in a wall.
There are 2 methods to get outside the boundary: transport there (if you have that permission), and dismount from transportation. Getting off a boat or a minecart may put you outside the boundary. If the boat or minecart are still in position, you may remount it, and reenter the world.
Villagers may not pass through the boundary. However, it is possible to trade across it.
Water passes through the boundary.
Arrows pass through the boundary.
Trees grow through the boundary.
I believe when blocks are destroyed, their remains may end up across the boundary. I believe if you get close enough you can capture it.
I have yet to observe monsters across a boundary, and I suspect I can be shot, but I don’t know if a creeper can blow me up. (I’m not sure I want to find out).

Dynamite will destroy blocks across the boundary.  Water may be poured across the boundary (and fetched.)  A creeper blowing up on my side of the boundary did not seem to destroy blocks across it.