Where in a Manifest goes an AnnotationCollection targeting multiple Canvases?

[robcast]

While writing a cookbook recipe on how to use AnnotationCollections https://github.com/IIIF/cookbook-recipes/issues/309 the question arose where it is allowed to put an AnnotationCollection in a Manifest.

The spec explicitly mentions an AnnotationCollection as the content of the supplementary property of a Range for "Annotations that target areas of Canvases within the Range and link content resources to those Canvases" but this limitation and the need to create a Range does not fit all use-cases.

There are quite a few use-cases where a large number of Annotations for multiple Canvases in a Manifest have been collected, e.g. from crowd-sourced transcription or machine learning classification processes. It would be useful to link these Annotations as AnnotationCollections on the Manifest level so that a viewer can offer to show these Annotations as distinct optional "layers" over all images in the Manifest.

We had some discussions if it would be allowed to put an AnnotationCollection with Annotations targeting multiple Canvases in the annotations property of a Manifest but the language of the spec does not seem to indicate that this is allowed.