This is why I raised an eyebrow when TFA wrote,

> When I saw this, I wondered why it has several inner hashes instead of using the raw string.

The inner hash constrains the alphabet on that portion of the input to the outer hash, thus easily letting you use a separator like "," or "|" without having to deal with the alphabet of the inner input, since it gets run through a hash. That is, for a very simplistic use case of two inputs a & b:

  sha256(','.join(
    [sha256(a), sha256(b)]
  ))

Now … whether that's why there was an inner hash at that point in TFA's code is another question, but I don't think one should dismiss inner hashes altogether.

Thanks—that makes sense. I was struggling to come up with an example that would fail but I was just unconsciously assuming the separator wasn’t showing up naturally in the individual parts instead of explicitly considering that as a prerequisite.