Hi Pieter,

> The human-readable part, which is intended to convey the type of data, or anything else that is relevant to the reader. This part MUST contain 1 to 83 US-ASCII characters, with each character having a value in the range [33-126]. HRP validity may be further restricted by specific applications.

You should also add to this section that the HRP should be lowercase.

Since Bech32 forbids mixed-case and otherwise converts everything to lowercase, it is good to warn upfront against using uppercase in the HRP.

I know the BIP is marked as final, but this wouldn't be a normative change.