You can read about map records on the last update.

Today's changes aims to some internal changes for offline players, map records and pre-1.13 fixes.

• Better Callback results for maps.
• Fixed whitelisted and blacklisted commands system.
  • Yes, it's finally here, sorry about that I didn't even notice that this system wasn't working properly.
• Internal changes on how map records and offline players are updated.
• Fixed block data issues on pre-1.13 versions.