Is there a solaris documentation online? I would expect Oracle to have put it behind a paywall.

It is indeed online, sans paywall: https://docs.oracle.com/en/operating-systems/solaris.html

Of course, with some Illumos distributions/derivatives/whatever-we're-calling-them, things are different due to using different tools or otherwise deviating from upstream Solaris. Better to start with your specific distro's documentation and use Oracle's Solaris docs to fill in the gaps, adjusting as necessary.