Disallow adding new properties to some objects?

[jonblower]

Mostly it's OK in JSON to allow additional properties to be added (particularly to allow extra metadata at a high level) but sometimes it wouldn't really make sense to do so (e.g. with a regularly-spaced axis object).

The spec doesn't say anything about this - perhaps it should in places.

[letmaik]

The spec has "... MAY have any number of members (name/value pairs)." in a few places:

• Parameter objects,
• ParameterGroup objects,
• CoverageJSON objects (Domain, NdArray, TiledNdArray, Coverage, CoverageCollection).

In other places there's "Custom values MAY be used as detailed in the “Extensions” section." which refers to custom members really.

I agree that it'd be worth to go over this and clean it up.