Cross-collection item search not possible.

[m-mohr]

If I use croll-collection item search (i.e. /search) and don't provide a collection, I get a HTTP 422 error stating that collection is required.
This makes a cross-collection item search impossible and is against the purpose of this endpoint, so I'd say it's not compliant with the stac-api-spec.

[FlorisCalkoen]

I can't remember the exact source/link but this was implemented by PC about a yr ago on purpose