This section introduces a syntax "[u]" for user messages and "[s]" for "(pull} signals". For a user messages there may be multiple types of signals: pull, error, receipt. These have different configurations, so there needs to be a way to differentiate them. For example, syntax "[r]", "[p]", "[e]".
With such a syntax, some other parameters could be dropped. For example:
Could be expressed as PMode[e].Protocol.Address
To express that an error is to be signed, we could use parameters:
This is the approach taken in CPPA3 with its concept of ebMS3Channel.
It is more general and more expressive.