Optional/Mandatory Requirement For ‘req’ Command Configuration File Options Missing In OpenSSL v1.1.1g Manual Pages?

The OpenSSL v1.1.1 manual page for the req command’s Configuration File Format options seems to be missing any mention about whether each option is mandatory or optional. The other OpenSSL command manual pages (ca and ts) that support configuration file usage do stipulate whether each configuration file option is mandatory or optional.

Does anyone know which req configuration file options are mandatory and which are optional?