BUG #16989: parameter track_commit_timestamp's category problem

The following bug has been logged on the website:

Bug reference: 16989
Logged by: yanliang lei
Email address: leiyanliang(at)highgo(dot)com
PostgreSQL version: 13.1
Operating system: CentOS7.6
Description:

In the following sql statement， parameter track_commit_timestamp's category
is Replication，and this “Replication” is a first-level category，and this
“Replication”has four second-level categories。

postgres=# select category from pg_settings where
name='track_commit_timestamp';
-[ RECORD 1 ]---------
category | Replication

postgres=#

In the document（ postgresql.org/docs/13/runtime-config-replication.html），
parameter track_commit_timestamp is in the “Sending Servers” category
，and，this “Sending Servers” is a second-level category。

so， what is the track_commit_timestamp’s category？