Came here to say this. Learning BNF ( https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form ) and knowing how to go to the roots have helped me more than once in my career (started as tester, moved to security engineer, then net engineer, then CISSP, then ISSO, then HIPPA SPO -- now senior sec engineer at top10 UNI)

Here is a good site to see what obsoletes and is superseded by what. https://www.potaroo.net/ietf/html/rfcindex.html