A selector within SpecificResource may not exist

[jptmoore]

Currently the schema specifies that both source and selector are required in SpecificResource.

The Web Annotation Data Model says that there MAY be 0 or more selector relationships associated with a Specific Resource so the annotation body could be:

{
"@context": "http://www.w3.org/ns/anno.jsonld",
"id": "http://example.org/anno18",
"type": "Annotation",
"body": {
"type": "SpecificResource",
"purpose": "tagging",
"source": "http://example.org/city1"
},
"target": {
"id": "http://example.org/photo1",
"type": "Image"
}
}

or as shown in the cookbook recipe https://iiif.io/api/cookbook/recipe/0022-linking-with-a-hotspot/manifest.json