No way to distinguish image and labels-image groups in 0.5

In version 0.4, it was possible to tell whether a group was a image group or an image labels group, because an image labels group was required to have a image-label entry in the metadata (https://ngff.openmicroscopy.org/0.4/index.html#label-md).

In version 0.5, it is no longer possible to distinguish between these two types of group, because image labels are no longer required to have an image-label entry. Instead, the spec only says this entry should (not must) be present. (https://ngff.openmicroscopy.org/0.5/index.html#labels-md).

This means that every valid image group is also a valid image-label group, and vice versa.

Would it be useful to still distinguish between these two types of group, and if so, introduce some new metadata that allows them to be distinguished?

Personally I think there is value in distinguishing between these groups so they can be interpreted differently by image veiwers (a labels dataset should be displayed differently to an imaging dataset for example) and readers, and for scientists to signal their intent as to whether a group is an image or labels.

Start by comparing the 0.4 label metadata section with the 0.5 labels metadata section linked in the issue. Determine whether the specification needs an unambiguous distinction between image and image-label groups, and document the agreed metadata rule or resolution in the relevant 0.5 specification text.