EntityPlayer player = ... // get the player entity int guiId = 1; // the identifier of the GUI to open World world = player.world; // get the world object the player is in BlockPos pos = new BlockPos(...); // the block position to open GUI at world.getServer().getPlayerList().getPlayer(player.getName()).openGui(modInstance, guiId, world, pos.getX(), pos.getY(), pos.getZ());In this example, we first obtain the player entity that we want to open the GUI for. We then define an identifier (guiId) for the GUI to be opened. Next, we get the World object that the player is currently in, and define a block position (pos) where the GUI should be opened. Finally, we call the openGui method on the player entity, passing the mod instance, guiId, world, and the x, y, and z positions. The exact package library used to implement the openGui method may vary based on the Minecraft mod developer's specific environment, but it is typically found within the `net.minecraft.entity.player` package.