reverted:
--- b/core/lib/Drupal/Core/Render/Renderer.php
+++ a/core/lib/Drupal/Core/Render/Renderer.php
@@ -320,10 +320,9 @@
         '#lazy_builder',
         '#cache',
         '#create_placeholder',
+        // These keys are not actually supported, but they are added automatically
+        // by the Renderer, so we don't crash on them; them being missing when
+        // their #lazy_builder callback is invoked won't surprise the developer.
-        // These keys are not actually supported, but they are added
-        // automatically by the Renderer.If they are missing when their
-        // #lazy_builder callback is invoked, it won't surprise the
-        // developer.
         '#weight',
         '#printed'
       ];