The example is starting from a WIF key and generating a master xpriv, which is perfectly fine (though I guess it is a pretty weird thing to do .... the point I believe was to demo how to create a BIP32 derivation starting from a master seed, and we may have reached for WIF because it was handy, not because it was a normal/wise way to store a seed).

What it does not do, and can't do, is derive any non-master xpriv, and you cannot convert xpriv -> WIF -> xpriv in this way.

I think we should hex-encode the master seed in our example. Agreed that using WIF here is confusing and potentially misleading.

Originally posted by @apoelstra in #745 (comment)