Description
The Search API doesn't require a target, as the scope is the resource that it's associated with.
The Web Annotation protocol doesn't specify any sort of search capabilities, though leaves the door open for additional query parameters when making GET requests to an endpoint.
So there's a gap into which annotation clients fall, when they want to ask a general endpoint for all annotations on a particular target resource. This happens (for example) when Mirador initializes a canvas with the annotations visible -- it makes a request for annotations on that canvas if there's an annotation endpoint configured.
IIIF should establish best practice in the lack of any other specification so that we don't have incompatible systems for this one feature. Then Mirador can drop its adapter pattern. That best practice should not conflict with the search API (of course) nor the WA protocol.
My proposal is to reserve ?target=(uri)