diff -u b/core/misc/form.js b/core/misc/form.js
--- b/core/misc/form.js
+++ b/core/misc/form.js
@@ -66,35 +66,35 @@
  * prevented, unless the form values are different to the previously submitted
  * values.
  *
- * A vastly simplified re-implementation of user-agent UX behavior that should
- * be natively supported by major web browsers, but at this point in time, only
- * Mozilla Firefox has a built-in protection.
+ * This is a simplified re-implementation of a user-agent behavior that should
+ * be natively supported by major web browsers, but at this time, only Firefox
+ * has a built-in protection.
  *
  * A form value-based approach ensures that the constraint is triggered for
- * consecutive, identical form submissions only. A form button-based approach
- * (1) would rely on [visible] buttons to exist where technically not required
- * and (2) would require more complex state management if there are multiple
- * buttons in a form.
+ * consecutive, identical form submissions only. Compared to that, a form
+ * button-based approach would (1) rely on [visible] buttons to exist where
+ * technically not required and (2) require more complex state management if
+ * there are multiple buttons in a form.
  *
  * This implementation is based on form-level submit events only and relies on
- * jQuery's (limited) serialize() method to determine submitted form values.
- * As such, the following limitations exist:
+ * jQuery's serialize() method to determine submitted form values. As such, the
+ * following limitations exist:
  *
  * - Event handlers on form buttons that preventDefault() do not receive a
  *   double-submit protection. That is deemed to be fine, since such button
  *   events typically trigger reversible client-side or server-side operations
  *   that are local to the context of a form only.
- * - Changed values in advanced form controls, such as file or image elements,
- *   are not part of the form values being compared between consecutive form
- *   submits (due to limitations of jQuery.serialize()). That is deemed to be
- *   acceptable, because if the user forgot to attach a file, then the size of
- *   HTTP payload will most likely be small enough to be fully passed to the
- *   server-side endpoint within (milli)seconds. If the user mistakenly attached
- *   a wrong file and is technically versed enough to manage to cancel the form
- *   submission (and HTTP payload) in order to attach a different file, then,
- *   bad luck, that 0.1% edge-case is not supported here.
+ * - Changed values in advanced form controls, such as file inputs, are not part
+ *   of the form values being compared between consecutive form submits (due to
+ *   limitations of jQuery.serialize()). That is deemed to be acceptable,
+ *   because if the user forgot to attach a file, then the size of HTTP payload
+ *   will most likely be small enough to be fully passed to the server endpoint
+ *   within (milli)seconds. If a user mistakenly attached a wrong file and is
+ *   technically versed enough to cancel the form submission (and HTTP payload)
+ *   in order to attach a different file, then that edge-case is not supported
+ *   here.
  *
- * Lastly, all forms using method="GET" are idempotent by definition of HTTP
+ * Lastly, all forms submitted via HTTP GET are idempotent by definition of HTTP
  * standards, so excluded in this implementation.
  */
 Drupal.behaviors.formSingleSubmit = {
@@ -111,7 +111,8 @@
       }
     }
 
-    $('body').once('form-single-submit').on('submit.singleSubmit', 'form:not([method~="GET"])', onFormSubmit);
+    $('body').once('form-single-submit')
+      .on('submit.singleSubmit', 'form:not([method~="GET"])', onFormSubmit);
   }
 };