diff --git a/core/config/schema/core.data_types.schema.yml b/core/config/schema/core.data_types.schema.yml
index 676b6ba..4035c86 100644
--- a/core/config/schema/core.data_types.schema.yml
+++ b/core/config/schema/core.data_types.schema.yml
@@ -208,7 +208,7 @@ route:
           label: 'Param'
 
 # Config dependencies.
-config_dependencies_calculated:
+config_dependencies_base:
   type: mapping
   mapping:
     entity:
@@ -228,11 +228,11 @@ config_dependencies_calculated:
         - type: string
 
 config_dependencies:
-  type: config_dependencies_calculated
+  type: config_dependencies_base
   label: 'Configuration dependencies'
   mapping:
     fixed:
-      type: config_dependencies_calculated
+      type: config_dependencies_base
       label: 'Fixed configuration dependencies'
 
 config_entity:
diff --git a/core/lib/Drupal/Core/Config/Entity/ConfigDependencyManager.php b/core/lib/Drupal/Core/Config/Entity/ConfigDependencyManager.php
index 84a0462..ba6d204 100644
--- a/core/lib/Drupal/Core/Config/Entity/ConfigDependencyManager.php
+++ b/core/lib/Drupal/Core/Config/Entity/ConfigDependencyManager.php
@@ -19,6 +19,27 @@
  * handled in the correct order. For example, node types are created before
  * their fields, and both are created before the view display configuration.
  *
+ * The configuration dependency value is structured like so:
+ * <code>
+ * array(
+ *   'config => array(
+ *     // An array of configuration entity object names.
+ *   ),
+ *   'module' => array(
+ *     // An array of module names.
+ *   ),
+ *   'theme' => array(
+ *     // An array of theme names.
+ *   ),
+ *   'fixed' => array(
+ *     // An array of fixed configuration dependencies.
+ *     'config' => array(),
+ *     'module' => array(),
+ *     'theme' => array(),
+ *   ),
+ * );
+ * </code>
+ *
  * If a configuration entity is provided as default configuration by an
  * extension (module, theme, or profile), the extension has to depend on any
  * modules or themes that the configuration depends on. For example, if a view
@@ -28,7 +49,11 @@
  * depend on a particular module that one of its default configuration entities
  * depends on, you can use a sub-module: move the configuration entity to the
  * sub-module instead of including it in the main extension, and declare the
- * module dependency in the sub-module only.
+ * module dependency in the sub-module only. If the extension author wants the
+ * configuration to depend on something that is not calculable then they can add
+ * these dependencies to the fixed dependency key. For example, the forum module
+ * provides the forum node type and in order for it to be deleted when the forum
+ * module is uninstalled it has a fixed dependency on the module.
  *
  * Classes for configuration entities with dependencies normally extend
  * \Drupal\Core\Config\Entity\ConfigEntityBase or at least use
@@ -37,11 +62,11 @@
  * \Drupal\Core\Config\Entity\ConfigEntityInterface::calculateDependencies(),
  * which should calculate (and return) the dependencies. In this method, use
  * \Drupal\Core\Config\Entity\ConfigEntityBase::addDependency() to add
- * dependencies. Most implementations call
+ * dependencies. Implementations should call
  * \Drupal\Core\Config\Entity\ConfigEntityBase::calculateDependencies() since it
  * provides a generic implementation that will discover dependencies due to
- * plugins and third party settings. To get a configuration entity's current
- * dependencies without forcing a recalculation use
+ * fixed dependencies, plugins, and third party settings. To get a configuration
+ * entity's current dependencies without forcing a recalculation use
  * \Drupal\Core\Config\Entity\ConfigEntityInterface::getDependencies().
  *
  * Classes for configurable plugins are a special case. They can either declare