core/modules/system/src/Plugin/Block/SystemPageActionsBlock.php  | 8 +++++---
 core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php | 5 +++--
 core/modules/system/src/Plugin/Block/SystemPageTabsBlock.php     | 8 +++++---
 core/modules/system/src/Plugin/Block/SystemPageTitleBlock.php    | 6 +++---
 4 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/core/modules/system/src/Plugin/Block/SystemPageActionsBlock.php b/core/modules/system/src/Plugin/Block/SystemPageActionsBlock.php
index 3c234a1..813da5a 100644
--- a/core/modules/system/src/Plugin/Block/SystemPageActionsBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemPageActionsBlock.php
@@ -115,9 +115,9 @@ public function build() {
   public function buildConfigurationForm(array $form, array &$form_state) {
     $form = parent::buildConfigurationForm($form, $form_state);
 
-    // The page actions block is never cacheable, because it may be dynamic.
+    // The "Page actions" block is never cacheable, due to access checking.
     $form['cache']['#disabled'] = TRUE;
-    $form['cache']['#description'] = $this->t('This block is never cacheable, it is not configurable.');
+    $form['cache']['#description'] = $this->t('This block is never cacheable because access checking is needed, it is not configurable.');
     $form['cache']['max_age']['#value'] = 0;
 
     return $form;
@@ -127,7 +127,9 @@ public function buildConfigurationForm(array $form, array &$form_state) {
    * {@inheritdoc}
    */
   public function isCacheable() {
-    // The page actions block is never cacheable, because it may be dynamic.
+    // The "Page Actions" block is never cacheable, because its contents depends
+    // on access checks, which are currently uncacheable.
+    // @todo Make cacheable once https://drupal.org/node/2287071 lands.
     return FALSE;
   }
 
diff --git a/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php b/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php
index 202f203..ad9e237 100644
--- a/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemPageMessagesBlock.php
@@ -114,7 +114,7 @@ public function getMessages($element) {
   public function buildConfigurationForm(array $form, array &$form_state) {
     $form = parent::buildConfigurationForm($form, $form_state);
 
-    // The page messages block is never cacheable, because it may be dynamic.
+    // @see ::isCacheable()
     $form['cache']['#disabled'] = TRUE;
     $form['cache']['#description'] = $this->t('This block is never cacheable, it is not configurable.');
     $form['cache']['max_age']['#value'] = 0;
@@ -126,7 +126,8 @@ public function buildConfigurationForm(array $form, array &$form_state) {
    * {@inheritdoc}
    */
   public function isCacheable() {
-    // The page messages block is never cacheable, because it may be dynamic.
+    // The page messages block is never cacheable, because its contents are
+    // session-specific and caching is useless.
     return FALSE;
   }
 
diff --git a/core/modules/system/src/Plugin/Block/SystemPageTabsBlock.php b/core/modules/system/src/Plugin/Block/SystemPageTabsBlock.php
index 67e737b..bd9ac2c 100644
--- a/core/modules/system/src/Plugin/Block/SystemPageTabsBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemPageTabsBlock.php
@@ -81,9 +81,9 @@ public function build() {
   public function buildConfigurationForm(array $form, array &$form_state) {
     $form = parent::buildConfigurationForm($form, $form_state);
 
-    // The page tabs block is never cacheable, because it may be dynamic.
+    // The "Page tabs" block is never cacheable, due to access checking.
     $form['cache']['#disabled'] = TRUE;
-    $form['cache']['#description'] = $this->t('This block is never cacheable, it is not configurable.');
+    $form['cache']['#description'] = $this->t('This block is never cacheable because access checking is needed, it is not configurable.');
     $form['cache']['max_age']['#value'] = 0;
 
     return $form;
@@ -93,7 +93,9 @@ public function buildConfigurationForm(array $form, array &$form_state) {
    * {@inheritdoc}
    */
   public function isCacheable() {
-    // The page tabs block is never cacheable, because it may be dynamic.
+    // The "Page Tabs" block is never cacheable, because its contents depends
+    // on access checks, which are currently uncacheable.
+    // @todo Make cacheable once https://drupal.org/node/2287071 lands.
     return FALSE;
   }
 
diff --git a/core/modules/system/src/Plugin/Block/SystemPageTitleBlock.php b/core/modules/system/src/Plugin/Block/SystemPageTitleBlock.php
index a198c0c..b3b6c86 100644
--- a/core/modules/system/src/Plugin/Block/SystemPageTitleBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemPageTitleBlock.php
@@ -116,9 +116,9 @@ public function build() {
   public function buildConfigurationForm(array $form, array &$form_state) {
     $form = parent::buildConfigurationForm($form, $form_state);
 
-    // The page title block is never cacheable, because it may be dynamic.
+    // The 'Page title' block is never cacheable, because it may be dynamic.
     $form['cache']['#disabled'] = TRUE;
-    $form['cache']['#description'] = $this->t('This block is never cacheable, it is not configurable.');
+    $form['cache']['#description'] = t('This block is never cacheable, it is not configurable.');
     $form['cache']['max_age']['#value'] = 0;
 
     return $form;
@@ -128,7 +128,7 @@ public function buildConfigurationForm(array $form, array &$form_state) {
    * {@inheritdoc}
    */
   public function isCacheable() {
-    // The page title block is never cacheable, because it may be dynamic.
+    // The 'Page title' block is never cacheable, because it may be dynamic.
     return FALSE;
   }