No Subject

3.1.2. To Element
The REQUIRED element is used to specify the ultimate receiver node of the
message known to the sender.
The value of this element MUST be a URI as defined in [RFC 2396].

2. Keep from/to optional and clarify definitions.

3. Remove from/to.

We need to talk about this further.
Action to Iwasa to justify why we need this in the spec, even as an option.
If it not justified, we can remove it at the next meeting.
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