diff --git a/core/modules/field/field.attach.inc b/core/modules/field/field.attach.inc
index 29ebd3b..7e66eb5 100644
--- a/core/modules/field/field.attach.inc
+++ b/core/modules/field/field.attach.inc
@@ -123,9 +123,9 @@
  *   which the method should be invoked.
  * @param Drupal\Core\Entity\EntityInterface $entity
  *   The fully formed $entity_type entity.
- * @param mixed $a
+ * @param array|string $a
  *   (optional) A parameter for the invoked method. Defaults to NULL.
- * @param mixed $b
+ * @param array|string $b
  *   (optional) A parameter for the invoked method. Defaults to NULL.
  * @param array $options
  *   (optional) An associative array of additional options, with the following
@@ -213,9 +213,9 @@ function field_invoke_method($method, $target_function, EntityInterface $entity,
  *   which the method should be invoked.
  * @param array $entities
  *   An array of entities, keyed by entity ID.
- * @param mixed $a
+ * @param array|string $a
  *   (optional) A parameter for the invoked method. Defaults to NULL.
- * @param mixed $b
+ * @param array|string $b
  *   (optional) A parameter for the invoked method. Defaults to NULL.
  * @param $options
  *   (optional) An associative array of additional options, with the following
@@ -717,9 +717,12 @@ function _field_invoke_widget_target() {
 /**
  * Defines a 'target function' for field_invoke_method().
  *
- * Used to invoke methods on an instance's formatter.
+ * Used to invoke methods on an instance's formatter. 
+ * Here we are using closure. 'use' is employed to use variables outside closure.
+ * use is always early binding implying that the variable values are just
+ * copied and modifying it inside the closure has no external effect.
  *
- * @param mixed $display
+ * @param  string|array $display
  *   Can be either:
  *   - The name of a view mode.
  *   - An array of display properties, as found in
@@ -729,6 +732,7 @@ function _field_invoke_widget_target() {
  *   A 'target function' for field_invoke_method().
  */
 function _field_invoke_formatter_target($display) {
+  //the anonymous function is made to use the external variable $display employing 'use'
   return function ($instance) use ($display) {
     return $instance->getFormatter($display);
   };
diff --git a/core/modules/field/lib/Drupal/field/FieldInstance.php b/core/modules/field/lib/Drupal/field/FieldInstance.php
index a1e7a4f..9547333 100644
--- a/core/modules/field/lib/Drupal/field/FieldInstance.php
+++ b/core/modules/field/lib/Drupal/field/FieldInstance.php
@@ -77,7 +77,7 @@ public function getWidget() {
   /**
    * Returns a Formatter plugin for the instance.
    *
-   * @param mixed $display_properties
+   * @param array|string $display_properties
    *   Can be either:
    *   - The name of a view mode.
    *   - An array of display properties, as found in the 'display' entry of