Clarify Will Delay Interval can appear in the PUBLISH packet send by the broker

[Takatoshi Kondo <redboltz@gmail.com>]

Hi,

I found inconsistent description between Will Delay Interval property
and Subscription Identifier property.

See the following description:

2.2.2.2 Property
https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc464547805

According to the Table 2-4 - Properties

Subscription Identifier can appear in PUBLISH and SUBSCRIBE.
Will Delay Interval can appear in Will Properties.

Clients cannot use Subscription Identifier with PUBLISH packet, but
the broker can add Subscription Identifier to he PUBLISH packet.
In this case, PUBLISH is in "Packet / Will Properties" column in the table.

Similarly, clients cannot use Will Delay Interval with PUBLISH packet,
but when the broker sends the Will Message as a PUBLISH packet, Will
Properties are added as PUBLISH properties.
If Will Delay Interval should be sent as PUBLISH property like other
Will Properties, PUBLISH should be added to the "Packet / Will
Properties" column in the table.

I also think that the purpose of Will Delay Interval is changing the
broker's behavior, and it is not so useful if the Will Delay Interval
is sent to the client.
I think that it is reasonable that if the broker removes Will Delay
Interval from the Will Properties but remains other Will Properties.
However, I couldn't find such a description.

There are two possible fixes:
1. Add PUBLISH to the "Packet / Will Properties" column "Will Delay
Interval" row in the table. or
2. Add the description something like "When Will Message is sent, Will
Delay Interval should be removed by the broker."

Any ideas?


----
Thanks,
Takatoshi