Why does this hot standy archive_command work

While learning a bit about basic hot standby configuration, I was reviewing an article that used these parameters

wal_level = 'hot_standby'
archive_mode = on
archive_command = 'cd .'
max_wal_senders = 1
hot_standby = on

How or why that particular archive_command actually works (... and it does ... I tried it ...) is not clear to me based on reading of the Postgresql documentation on this topic. I would have expected to see an actual copy or rsync command, as described in the fine manual at section 25.3.1. "Setting Up WAL Archiving"

The entire example appears at

https://www.digitalocean.com/community/tutorials/how-to-set-up-master-slave-replication-on-postgresql-on-an-ubuntu-12-04-vps

Can anyone enlighten on this topic, or provide a link to an existing explanation?

-- B