docs: def fancy(cls, contains, max_tries, inner=False, keepcase=False):
          """
          Try to create a key with a chosen prefix, by starting with a 26-bit
          urandom number and appending with 8-byte integers until prefix matches.
          This function is naive, but has a max_tries argument which will abort when
          reached with a ValueError.
          TODO: make this smarter, in general. Variable byte length according to
          expected attempts, warnings of expected duration of iteration, etc. 
          TODO: Implement multiprocessing to use poly-core machines fully:
              - Shared list, each process checks if empty every cycle, aborts if
                contains a value.
              - Successful values are pushed to list, cancelling all processes?
              - Server waits on all child processes then expects a list?
              - Ensure child processes start with different random base numbers,
                to avoid duplication?
              - Investigate server/manager aspect of multiprocessing; mini-clustering?
          """
          contains = contains if keepcase else contains.lower()
          if not set(contains).issubset(base58.alphabet):
              raise ValueError("Cannot find contained phrase '{}' as it contains non-b58 characters".format(contains))
          basenum = os.urandom(26)
          for i in range(max_tries):
              k = nacl.public.PrivateKey(basenum + i.to_bytes(6, 'big'))
              ukey = cls(k.public_key, k)
              test_uid = ukey.userID if keepcase else ukey.userID.lower()
              if test_uid.startswith(contains) or test_uid.endswith(contains) or (inner and contains in test_uid):
                  return ukey
          else:
              raise ValueError("Could not create key with desired prefix '{}' in {} attempts.".format(prefix, max_tries))