diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeCustomFormatter.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeCustomFormatter.php
index 45cf665..1834d4c 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeCustomFormatter.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeCustomFormatter.php
@@ -10,7 +10,10 @@
 /**
  * Plugin implementation of the 'Custom' formatter for 'daterange' fields.
  *
- * @FieldFormatter(
+ * This formatter renders the data range as plain text, with fully
+ * configurable a date format using the PHP date syntax and separator.
+ *
+* @FieldFormatter(
  *   id = "daterange_custom",
  *   label = @Translation("Custom"),
  *   field_types = {
diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php
index 1469bd4..9006fc8 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php
@@ -10,6 +10,10 @@
 /**
  * Plugin implementation of the 'Default' formatter for 'daterange' fields.
  *
+ * This formatter renders the data range using <time> elements, with
+ * configurable date formats (from the list of configured formats) and
+ * separator.
+ *
  * @FieldFormatter(
  *   id = "daterange_default",
  *   label = @Translation("Default"),
diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangePlainFormatter.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangePlainFormatter.php
index a2a1b13..5bdcc6a 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangePlainFormatter.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateRangePlainFormatter.php
@@ -8,6 +8,9 @@
 /**
  * Plugin implementation of the 'Plain' formatter for 'daterange' fields.
  *
+ * This formatter renders the data range as a plain text string, with a
+ * configurable separator using an ISO-like date format string.
+ *
  * @FieldFormatter(
  *   id = "daterange_plain",
  *   label = @Translation("Plain"),
diff --git a/core/modules/datetime/src/Plugin/Field/FieldType/DateRangeItem.php b/core/modules/datetime/src/Plugin/Field/FieldType/DateRangeItem.php
index 78e2cb8..dfe036f 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldType/DateRangeItem.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldType/DateRangeItem.php
@@ -169,4 +169,12 @@ public function onChange($property_name, $notify = TRUE) {
     parent::onChange($property_name, $notify);
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public static function mainPropertyName() {
+    // A date range item is a compound value, so there is no main property name.
+    return NULL;
+  }
+
 }
diff --git a/core/modules/datetime/src/Tests/DateRangeFieldTest.php b/core/modules/datetime/src/Tests/DateRangeFieldTest.php
index 1aa3775..512840a 100644
--- a/core/modules/datetime/src/Tests/DateRangeFieldTest.php
+++ b/core/modules/datetime/src/Tests/DateRangeFieldTest.php
@@ -537,45 +537,12 @@ function testDatelistWidget() {
     // Display creation form.
     $this->drupalGet('entity_test/add');
 
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value-year\"]", NULL, 'Year element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value-year", '', 'No year selected.');
-    $this->assertOptionByText("edit-$field_name-0-value-year", t('Year'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value-month\"]", NULL, 'Month element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value-month", '', 'No month selected.');
-    $this->assertOptionByText("edit-$field_name-0-value-month", t('Month'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value-day\"]", NULL, 'Day element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value-day", '', 'No day selected.');
-    $this->assertOptionByText("edit-$field_name-0-value-day", t('Day'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value-hour\"]", NULL, 'Hour element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value-hour", '', 'No hour selected.');
-    $this->assertOptionByText("edit-$field_name-0-value-hour", t('Hour'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value-minute\"]", NULL, 'Minute element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value-minute", '', 'No minute selected.');
-    $this->assertOptionByText("edit-$field_name-0-value-minute", t('Minute'));
-    $this->assertNoFieldByXPath("//*[@id=\"edit-$field_name-0-value-second\"]", NULL, 'Second element not found.');
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value-ampm\"]", NULL, 'AMPM element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value-ampm", '', 'No ampm selected.');
-    $this->assertOptionByText("edit-$field_name-0-value-ampm", t('AM/PM'));
-
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value2-year\"]", NULL, 'Year element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value2-year", '', 'No year selected.');
-    $this->assertOptionByText("edit-$field_name-0-value2-year", t('Year'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value2-month\"]", NULL, 'Month element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value2-month", '', 'No month selected.');
-    $this->assertOptionByText("edit-$field_name-0-value2-month", t('Month'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value2-day\"]", NULL, 'Day element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value2-day", '', 'No day selected.');
-    $this->assertOptionByText("edit-$field_name-0-value2-day", t('Day'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value2-hour\"]", NULL, 'Hour element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value2-hour", '', 'No hour selected.');
-    $this->assertOptionByText("edit-$field_name-0-value2-hour", t('Hour'));
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value2-minute\"]", NULL, 'Minute element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value2-minute", '', 'No minute selected.');
-    $this->assertOptionByText("edit-$field_name-0-value2-minute", t('Minute'));
-    $this->assertNoFieldByXPath("//*[@id=\"edit-$field_name-0-value2-second\"]", NULL, 'Second element not found.');
-    $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-value2-ampm\"]", NULL, 'AMPM element found.');
-    $this->assertOptionSelected("edit-$field_name-0-value2-ampm", '', 'No ampm selected.');
-    $this->assertOptionByText("edit-$field_name-0-value2-ampm", t('AM/PM'));
+    foreach (['value','value2'] as $column) {
+      foreach (['year', 'month', 'day', 'hour', 'minute', 'ampm'] as $element) {
+        $this->assertFieldByXPath("//*[@id=\"edit-$field_name-0-$column-$element\"]", NULL, $element . ' element found.');
+        $this->assertOptionSelected("edit-$field_name-0-value-year", '', 'No ' . $element . ' selected.');
+      }
+    }
 
     // Submit a valid date and ensure it is accepted.
     $start_date_value = ['year' => 2012, 'month' => 12, 'day' => 31, 'hour' => 5, 'minute' => 15];