bootstrap-vz/plugins/vagrant/manifest-schema.json

{
	"$schema": "http://json-schema.org/draft-04/schema#",
	"title": "Vagrant plugin manifest",
	"type": "object",
	"properties": {
		"provider": {
			"type": "string",
			"enum": ["virtualbox"]
		},
		"volume": {
			"type": "object",
			"properties": {
				"backing": {
					"type": "string",
					"enum": ["vmdk"]
					// VirtualBox only supports vmdk or raw when importing via OVF:
					// https://www.virtualbox.org/browser/vbox/trunk/src/VBox/Main/src-server/ApplianceImplImport.cpp#L636
				}
			},
			"required": ["backing"]
		}
	}
}