code: def sign(privkey_bundle, plaintext):
      
      if virtualchain.is_singlesig(privkey_bundle):
          return sign_singlesig(privkey_bundle, plaintext)
      elif virtualchain.is_multisig(privkey_bundle):
          return sign_multisig(privkey_bundle, plaintext)
      else:
          raise ValueError("private key bundle is neither a singlesig nor multisig bundle")
docs: Sign a subdomain plaintext with a private key bundle
      Returns the base64-encoded scriptsig