I learned most of what I know though a combination of just exploring at the REPL (making heavy use of the dump function and function docstrings) and asking around for help.
I generally find ‘reading the source’ to be somewhat unhelpful unless the source code is very naive and basic.
For instance, what I posted above is essentially the exact process of how I learned about the kwargs storage. Someone asked a similar question some moons ago and I was playing around with it, made a function that slurps up kwargs and returns them, then called dump on the output and saw that the original NamedTuple was hidden in the Pairs structure.