On what system does the postgresql docs run?

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/12/libpq-pgpass.html
Description:

Hi, I really like the postgresql documentation system and am curious what it
is.  After viewing source and digging around, I can't seem to determine what
it's running on.  To be clear I am asking what publishing system is used to
edit and publish a page like the one below:
https://www.postgresql.org/docs/12/libpq-pgpass.html

Thanks,
Winston