code: func createSpentDelegatedOutputKey(txID string, index int) (string, error) {
  	return createCompositeKey(tokenDelegatedInput, []string{txID, strconv.Itoa(index)})
  }
docs: // Create a ledger key for a spent individual delegated output in a token transaction, as a function of
  // the transaction ID, and the index of the delegated output