Suggestion for new control .unit to specify the physical unit of a field

[mstahl-iis]

This is the proposal for a new control .unit to specify the physical unit of a data field.

• Should be probably only allowed for numeric types
• Valid units should be at least the ones defined by International System of Units

[cabo]

I would expect the SenML registry of units (defined by RFC 8428 and RFC 8798) to be a good basis for anything like this, so I think we already are half way there.
However, I believe that adding an "annotation" feature like this goes beyond the current architecture of CDDL.
So I'd like to pick up discussion about how to use these "annotations" and what their general structure is, with more than .unit as an example to ponder.
On the way to that, a few worked examples how a (non-trivial) CDDL spec might make use of .unit and what tool support you expect would be very useful input!

[mstahl-iis]

SenML surely is a sensible choice.

Tools could make use of e.g. Boost.Units or Pint, though it seems both are not widely used.

The main point is probably to have a consistent rendering in documents that describe the specification.