diff --git a/core/modules/rest/src/Plugin/views/style/Serializer.php b/core/modules/rest/src/Plugin/views/style/Serializer.php
index c42f9bd545..32ba9130e2 100644
--- a/core/modules/rest/src/Plugin/views/style/Serializer.php
+++ b/core/modules/rest/src/Plugin/views/style/Serializer.php
@@ -125,6 +125,11 @@ public function render() {
     // which will transform it to arrays/scalars. If the Data field row plugin
     // is used, $rows will not contain objects and will pass directly to the
     // Encoder.
+    // XML encoding is unsupported in Drupal 8.3.x as XML encoding has no way to
+    // support a representation of multi-value fields. Single value fields can
+    // produce usable output, and usage with the DataFieldRow plugin (single
+    // values) will work as expected.
+    // @see \Drupal\serialization\Encoder\XmlEncoder
     foreach ($this->view->result as $row_index => $row) {
       $this->view->row_index = $row_index;
       $rows[] = $this->view->rowPlugin->render($row);
diff --git a/core/modules/serialization/src/Encoder/XmlEncoder.php b/core/modules/serialization/src/Encoder/XmlEncoder.php
index f5456d4b0e..6451e642db 100644
--- a/core/modules/serialization/src/Encoder/XmlEncoder.php
+++ b/core/modules/serialization/src/Encoder/XmlEncoder.php
@@ -13,7 +13,8 @@
  * implementing NormalizationAwareInterface, and can be normalized externally.
  *
  * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.0. This
- *   exists solely for BC, for classes extending this.
+ *   exists solely for BC, for classes extending this and existing usage that is
+ *   already configured to use or allowed the XML format.
  */
 class XmlEncoder implements EncoderInterface, DecoderInterface {