incremental backup

I use the new incremental option with pg_basebackup version 17. 
There are mainly two type of files in the result backup folder base:

1. INCREMENTAL.<oid> that is always 12 bytes and that could contain the a LSN and the checksum algorithm.
2. oid file that have a length of 0.

Somebody could explain to me why these empty files are present and how they are used in the mecanism of incremental backup?

Thanks for helping

Fabrice