add callback error unrolling test

demos/_unit-test/callback-nested.php

@@ -27,24 +27,33 @@
 $loader = Loader::addTo($app);
 $loader->loadEvent = false;
 
-$loader->set(function ($p) use ($m) {
-    $loader_1 = Loader::addTo($p);
-    $loader_1->loadEvent = false;
+$loader->set(function (Loader $p) use ($m) {
+    if (!empty($_GET['err_main_loader'])) {
+        throw new Exception('Exception from Main Loader');
+    }
+
+    $loaderSub = Loader::addTo($p);
+    $loaderSub->loadEvent = false;
 
     Header::addTo($p, ['Loader-1', 'size' => 4]);
 
-    $loader_1->set(function ($p) use ($m) {
+    $loaderSub->set(function (Loader $p) use ($m) {
+        if (!empty($_GET['err_sub_loader'])) {
+            throw new Exception('Exception from Sub Loader');
+        }
+
         Header::addTo($p, ['Loader-2', 'size' => 4]);
-        $loader_3 = Loader::addTo($p);
 
-        $loader_3->set(function ($p) use ($m) {
+        $loaderSubSub = Loader::addTo($p);
+
+        $loaderSubSub->set(function (Loader $p) use ($m) {
             Header::addTo($p, ['Loader-3', 'size' => 4]);
 
             $c = Crud::addTo($p, ['ipp' => 4]);
             $c->setModel($m, [$m->fieldName()->name]);
         });
     });
-    \Atk4\Ui\Button::addTo($p, ['Load2'])->js('click', $loader_1->jsLoad());
+    \Atk4\Ui\Button::addTo($p, ['Load2'])->js('click', $loaderSub->jsLoad());
 });
 
 \Atk4\Ui\Button::addTo($app, ['Load1'])->js('click', $loader->jsLoad());

src/Loader.php

@@ -21,7 +21,7 @@ class Loader extends View
     public $shim;
 
     /**
-     * Specify which event will cause Loader to begen fetching it's actual data. In some cases
+     * Specify which event will cause Loader to begin fetching it's actual data. In some cases
      * you would want to wait. You can set a custom JavaScript event name then trigger() it.
      *
      * Default value is `true` which means loading will take place as soon as possible. Setting this