What is the significance of a config value wrapped in parentheses in postgresql.conf?

Question

In a guide for tuning postgres for Nominatim OSM imports, the guide recommends the following settings being modified at the time of writing:

shared_buffers = 2GB
maintenance_work_mem = (10GB)
autovacuum_work_mem = 2GB
work_mem = (50MB)
effective_cache_size = (24GB)
synchronous_commit = off
checkpoint_segments = 100 # only for postgresql <= 9.4
max_wal_size = 1GB # postgresql > 9.4
checkpoint_timeout = 10min
checkpoint_completion_target = 0.9

When I tried to actually put them in parentheses, the values were throwing "invalid line" errors.

Error: invalid line 131 in /etc/postgresql/12/main/postgresql.conf: work_mem = (50MB)           # min 64kB

So here is my question: What is the significance/purpose of putting the values in parentheses? Is this just an error? If it's not an error, then how do I do it without getting an error?

Thanks in advance!

EDIT: Sorry if this is a question I could've figured out online, I promise I did try but I couldn't find anything.