XP Level Border Multiplayer

Bug fixes and improvements

• Fixed players spawning outside the world border
• Fixed the border only growing half a block instead of a full block in each direction
• Players may still spawn inside a block, but close to the surface
• Added a welcome message and sound effect
• Added a datapack icon (PNG)
• Updated the datapack description
• Existing worlds no longer strictly require traveling to 0 0, but it is still recommended for safety