diff --git a/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php b/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php
index fa3bafb..4d515a3 100644
--- a/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php
+++ b/core/lib/Drupal/Component/Discovery/YamlDirectoryDiscovery.php
@@ -33,14 +33,14 @@ class YamlDirectoryDiscovery implements DiscoverableInterface {
   protected $directories = [];
 
   /**
-   * The suffix the file cache key.
+   * The suffix for the file cache key.
    *
    * @var string
    */
   protected $fileCacheKeySuffix;
 
   /**
-   * The key which contains the value to key the data by.
+   * The key contained in the discovered data that identifies it.
    *
    * @var string
    */
@@ -50,7 +50,9 @@ class YamlDirectoryDiscovery implements DiscoverableInterface {
    * Constructs a YamlDirectoryDiscovery object.
    *
    * @param array $directories
-   *   An array of directories to scan, keyed by the provider.
+   *   An array of directories to scan, keyed by the provider. The value can
+   *   either be a string or an array of strings. The string values should be
+   *   the path of a directory to scan.
    * @param string $file_cache_key_suffix
    *   The file cache key suffix. This should be unique for each type of
    *   discovery.
@@ -144,9 +146,9 @@ protected function findFiles() {
   /**
    * Gets an iterator to loop over the files in the provided directory.
    *
-   * This method is exists so that it is easy to replace this functionality in
-   * a class that extends this one. For example, it could be used to make the
-   * scan recursive.
+   * This method exists so that it is easy to replace this functionality in a
+   * class that extends this one. For example, it could be used to make the scan
+   * recursive.
    *
    * @param string $directory
    *   The directory to scan.
diff --git a/core/lib/Drupal/Core/Plugin/Discovery/YamlDirectoryDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/YamlDirectoryDiscovery.php
index 244394e..2a5c1f6 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/YamlDirectoryDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/YamlDirectoryDiscovery.php
@@ -10,7 +10,7 @@
 use Drupal\Component\Discovery\YamlDirectoryDiscovery as ComponentYamlDirectoryDiscovery;
 
 /**
- * Allows directories that contain YAML files to define plugin definitions.
+ * Allows multiple YAML files per directory to define plugin definitions.
  */
 class YamlDirectoryDiscovery extends YamlDiscovery {
 
@@ -18,7 +18,9 @@ class YamlDirectoryDiscovery extends YamlDiscovery {
    * Constructs a YamlDirectoryDiscovery object.
    *
    * @param array $directories
-   *   An array of directories to scan, keyed by the provider.
+   *   An array of directories to scan, keyed by the provider. The value can
+   *   either be a string or an array of strings. The string values should be
+   *   the path of a directory to scan.
    * @param string $file_cache_key_suffix
    *   The file cache key suffix. This should be unique for each type of
    *   discovery.