func (d *Doc) Ref(r Ref) *Definition {
	if refIF, ok := r["$ref"]; ok {
		refKey := strings.TrimPrefix(refIF.(string), "#/definitions/")
		return d.Definitions[refKey]
	}
	return nil
}
func (d *Doc) Ref(r Ref) *Definition {
	if refIF, ok := r["$ref"]; ok {
		refKey := strings.TrimPrefix(refIF.(string), "#/definitions/")
		return d.Definitions[refKey]
	}
	return nil
}
// Ref gets a definition for a Schema reference, if it exists