Axis spec may need tightening

[jonblower]

• "If missing, the member "dataType" defaults to "primitive" and MUST not be included for that default case." - this is not clear to me
• Is coordinates required for tuples and polygon axes?
• Is bounds only valid for primitive-valued axes based on an array of values (I assume so)

[letmaik]

• "If missing, the member "dataType" defaults to "primitive" and MUST not be included for that default case." - this is not clear to me

It just means never include "dataType": "primitive". The reason for this is to enforce a canonical format. This is the same as for "timeScale" in "TemporalRS".

• Is coordinates required for tuples and polygon axes?

It is required whenever there is more than one coordinate, and this should be spelled out. Polygons always have two, and tuples at least one. The 1-tuple degenerate case should probably be discouraged in favour of using a primitive axis.

• Is bounds only valid for primitive-valued axes based on an array of values (I assume so)

In practice yes. I think we left it unconstrained in case there will be something non-primitive that could make use of it as well. I'm fine with tightening it up to make it clearer.