code: @GetMapping(value = "/{entityTypeId}/{id}/{refAttributeName}", produces = APPLICATION_JSON_VALUE)
    public Object retrieveEntityAttribute(
        @PathVariable("entityTypeId") String entityTypeId,
        @PathVariable("id") String untypedId,
        @PathVariable("refAttributeName") String refAttributeName,
        @Valid EntityCollectionRequest request,
        @RequestParam(value = "attributes", required = false) String[] attributes,
        @RequestParam(value = "expand", required = false) String[] attributeExpands) {
      Set<String> attributesSet = toAttributeSet(attributes);
      Map<String, Set<String>> attributeExpandSet = toExpandMap(attributeExpands);
  
      return retrieveEntityAttributeInternal(
          entityTypeId, untypedId, refAttributeName, request, attributesSet, attributeExpandSet);
    }
docs: Get's an XREF entity or a list of MREF entities
  
  <p>Example:
  
  <p>/api/v1/person/99/address