I'd like to export a derived private key from my Electrum HD wallet, and use it as a HD wallet master key in a Mycelium wallet.

I used `bx` to get the key like this (`m/2'/0`) (where `m` is the unencrypted `xprv` key extracted from default_wallet JSON):

    $ cat m | bx hd-private --index 2 --hard \
            | bx hd-private | bx hd-to-wif | qrencode -o - | feh -

And scanned the resulting QR code in Mycelium using the "Add Unrelated Account/Scan".

The wallet works, but it's treated as a "single-address" wallet, not a HD wallet. I presumed that the derived xprv can be used as a master key for deriving more keys, since it contains the chaincode. Is that not the case?

Also, the Mycelium "Add Unrelated Account" screen says that

> Scan Bitcoin address, private key or HD-Account.

What format does "HD-Account" mean? Is it WIF?