code: public static FieldScope fromSetFields(
        Message firstMessage, Message secondMessage, Message... rest) {
      return fromSetFields(asList(firstMessage, secondMessage, rest));
    }
docs: Creates a {@link FieldScope} covering the fields set in every message in the provided list of
  messages, with the same semantics as in {@link #fromSetFields(Message)}.
  
  <p>This can be thought of as the union of the {@link FieldScope}s for each individual message,
  or the {@link FieldScope} for the merge of all the messages. These are equivalent.