diff --git a/core/lib/Drupal/Core/Cache/Context/CacheContextInterface.php b/core/lib/Drupal/Core/Cache/Context/CacheContextInterface.php
index f7ce3ab..ce6947f 100644
--- a/core/lib/Drupal/Core/Cache/Context/CacheContextInterface.php
+++ b/core/lib/Drupal/Core/Cache/Context/CacheContextInterface.php
@@ -34,11 +34,14 @@ public function getContext();
   /**
    * Gets the cacheability metadata for the context.
    *
-   * If the cache context is being optimized away, cache tags and max-age
-   * provided by this method will be bubbled up into the cache item.
+   * There are three valid cases for the returned CacheableMetadata object:
+   * - An empty object means this can be optimized away safely.
+   * - A max-age of 0 means that this context can never be optimized away. It
+   *   will never bubble up and cache tags will not be used.
+   * - Any non-zero max-age and cache tags will bubble up into the cache item
+   *   if this is optimized away to allow for invalidation if the context
+   *   value changes.
    *
-   * If a max-age of 0 is returned then it means that this context can not
-   * be optimized away.
    *
    * @return \Drupal\Core\Cache\CacheableMetadata
    *   A cacheable metadata object.
diff --git a/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php b/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php
index a0b3b4e..4bf3459 100644
--- a/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php
+++ b/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\Core\Cache\Context;
 
-use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Cache\CacheableMetadata;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -104,7 +103,8 @@ public function getLabels($include_calculated_cache_contexts = FALSE) {
    *   The ContextCacheKeys object containing the converted cache keys and
    *   cacheability metadata.
    *
-   * @throws \InvalidArgumentException
+   * @throws \LogicException
+   *   Thrown if any of the context tokens or parameters are not valid.
    */
   public function convertTokensToKeys(array $context_tokens) {
     $this->validateTokens($context_tokens);
diff --git a/core/lib/Drupal/Core/Cache/Context/CalculatedCacheContextInterface.php b/core/lib/Drupal/Core/Cache/Context/CalculatedCacheContextInterface.php
index 5d38935..0647fad 100644
--- a/core/lib/Drupal/Core/Cache/Context/CalculatedCacheContextInterface.php
+++ b/core/lib/Drupal/Core/Cache/Context/CalculatedCacheContextInterface.php
@@ -34,23 +34,31 @@ public static function getLabel();
    * @return string
    *   The string representation of the cache context. When $parameter is NULL,
    *   a value representing all possible parameters must be generated.
+   *
+   * @throws \LogicException
+   *   Thrown if the passed in parameter is invalid.
    */
   public function getContext($parameter = NULL);
 
   /**
    * Gets the cacheability metadata for the context based on the parameter value.
    *
-   * If the cache context is being optimized away, cache tags and max-age
-   * provided by this method will be bubbled up into the cache item.
-   *
-   * If a max-age of 0 is returned then it means that this context can not
-   * be optimized away.
+   * There are three valid cases for the returned CacheableMetadata object:
+   * - An empty object means this can be optimized away safely.
+   * - A max-age of 0 means that this context can never be optimized away. It
+   *   will never bubble up and cache tags will not be used.
+   * - Any non-zero max-age and cache tags will bubble up into the cache item
+   *   if this is optimized away to allow for invalidation if the context
+   *   value changes.
    *
    * @param string|null $parameter
    *   The parameter, or NULL to indicate all possible parameter values.
    *
    * @return \Drupal\Core\Cache\CacheableMetadata
    *   A cacheable metadata object.
+   *
+   * @throws \LogicException
+   *   Thrown if the passed in parameter is invalid.
    */
   public function getCacheableMetadata($parameter = NULL);
 
diff --git a/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php b/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php
index 2d2a4d6..3ff2dc4 100644
--- a/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php
@@ -30,7 +30,7 @@ public static function getLabel() {
    */
   public function getContext($menu_name = NULL) {
     if (!$menu_name) {
-      throw new \InvalidArgumentException('No menu name provided for menu.active_trails cache context.');
+      throw new \LogicException('No menu name provided for menu.active_trails cache context.');
     }
 
     $active_trail = $this->container->get('menu.active_trail')
@@ -43,7 +43,7 @@ public function getContext($menu_name = NULL) {
    */
   public function getCacheableMetadata($menu_name = NULL) {
     if (!$menu_name) {
-      throw new \InvalidArgumentException('No menu name provided for menu.active_trails cache context.');
+      throw new \LogicException('No menu name provided for menu.active_trails cache context.');
     }
     $cacheable_metadata = new CacheableMetadata();
     return $cacheable_metadata->setCacheTags(["config:system.menu.$menu_name"]);
diff --git a/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php b/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php
index d6adff2..d6ffd13 100644
--- a/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php
+++ b/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php
@@ -11,6 +11,10 @@
 
 /**
  * Defines a base class for cache contexts depending only on the request stack.
+ *
+ * Subclasses need to implement either
+ * \Drupal\Core\Cache\Context\CacheContextInterface or
+ * \Drupal\Core\Cache\Context\CalculatedCacheContextInterface themself.
  */
 abstract class RequestStackCacheContextBase {
 
diff --git a/core/lib/Drupal/Core/Cache/Context/UserCacheContextBase.php b/core/lib/Drupal/Core/Cache/Context/UserCacheContextBase.php
index 0113295..602fde6 100644
--- a/core/lib/Drupal/Core/Cache/Context/UserCacheContextBase.php
+++ b/core/lib/Drupal/Core/Cache/Context/UserCacheContextBase.php
@@ -11,8 +11,12 @@
 
 /**
  * Base class for user-based cache contexts.
+ *
+ * Subclasses need to implement either
+ * \Drupal\Core\Cache\Context\CacheContextInterface or
+ * \Drupal\Core\Cache\Context\CalculatedCacheContextInterface themself.
  */
-abstract class UserCacheContextBase implements CacheContextInterface {
+abstract class UserCacheContextBase {
 
   /**
    * The account object.
diff --git a/core/modules/book/src/Cache/BookNavigationCacheContext.php b/core/modules/book/src/Cache/BookNavigationCacheContext.php
index 97a405e..9dbe1db 100644
--- a/core/modules/book/src/Cache/BookNavigationCacheContext.php
+++ b/core/modules/book/src/Cache/BookNavigationCacheContext.php
@@ -79,8 +79,8 @@ public function getCacheableMetadata() {
     // That information is however not stored as part of the node.
     $cacheable_metadata = new CacheableMetadata();
     if ($node = $this->requestStack->getCurrentRequest()->get('node')) {
-      // If the node is part of a book that we can use the cache tag for that
-      // book. If not, then we can't be optimized away.
+      // If the node is part of a book then we can use the cache tag for that
+      // book. If not, then it can't be optimized away.
       if (!empty($node->book['bid'])) {
         $cacheable_metadata->addCacheTags(['bid:' . $node->book['bid']]);
       }