diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index b873f6c..9911d02 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -8,6 +8,7 @@
 namespace Drupal\Core\Template;
 
 use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Component\Utility\String;
 
 /**
  * A class that can be used for collecting then rendering HTML attributtes.
@@ -76,7 +77,7 @@ public function offsetSet($name, $value) {
    * @param mixed $value
    *   The attribute value.
    *
-   * @throws \Exception
+   * @throws \UnexpectedValueException
    *   If invalid object was passed as a value.
    *
    * @return \Drupal\Core\Template\AttributeValueBase
@@ -107,7 +108,11 @@ protected function createAttributeValue($name, $value) {
     }
     // Provide a better exception message when invalid object is passed as value.
     elseif (is_object($value)) {
-      throw new \Exception('"' . $name . '" attribute value of type "' . get_class($value) . '" can not be converted to string');
+      throw new \UnexpectedValueException(String::format('"@name" attribute value of type "@type" can not be converted to string',
+        array(
+          '@name' => $name,
+          '@type' => get_class($value),
+        )));
     }
 
     return $value;
diff --git a/core/lib/Drupal/Core/Template/TwigNodeExpressionFunction.php b/core/lib/Drupal/Core/Template/TwigNodeExpressionFunction.php
index 3902abd..0e3f9b4 100644
--- a/core/lib/Drupal/Core/Template/TwigNodeExpressionFunction.php
+++ b/core/lib/Drupal/Core/Template/TwigNodeExpressionFunction.php
@@ -13,11 +13,16 @@
  * A class that extends Twig_Node_Expression_Function.
  *
  * Instances of this class are used in Drupal\Core\Template\TwigNodeVisitor
- * to call the render_var function, with extra arguments.
+ * to call the render_var function, with extra arguments - generic name of var.
  *
  * @see core\vendor\twig\twig\lib\Twig\Node\Expression\Function.php
  */
 class TwigNodeExpressionFunction extends \Twig_Node_Expression_Function {
+
+  /**
+   * @var array
+   *   Contains additional data that could be useful inside twig.engine.
+   */
   protected $extra_arguments;
 
   /**
@@ -41,6 +46,7 @@ public function compile(\Twig_Compiler $compiler) {
     $this->setAttribute('needs_environment', $function->needsEnvironment());
     $this->setAttribute('needs_context', $function->needsContext());
     $this->setAttribute('arguments', array_merge($function->getArguments(), $this->extra_arguments));
+
     if ($function instanceof \Twig_FunctionCallableInterface || $function instanceof \Twig_SimpleFunction) {
       $this->setAttribute('callable', $function->getCallable());
     }
@@ -48,4 +54,3 @@ public function compile(\Twig_Compiler $compiler) {
     $this->compileCallable($compiler);
   }
 }
-
diff --git a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
index 5eab437..55dd4de 100644
--- a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
@@ -229,7 +229,7 @@ public function testStorage() {
   }
 
   /**
-   * PHPUnit's data provider callback.
+   * Provides test data sets for testCreateAttributeValue().
    *
    * @see $this->testCreateAttributeValue()
    * @return array
@@ -297,30 +297,15 @@ public function testCreateAttributeValue($name, $value, $result) {
   }
 
   /**
-   * PHPUnit's data provider callback to test exceptions.
-   *
-   * @see $this->testCreateAttributeValueException()
-   * @return array
-   */
-  public function createAttributeValueExceptionProvider() {
-    $testCases = array();
-
-    // Test passed object without 'class' as name.
-    $name = $this->getRandomGenerator()->string();
-    $value = $this->getRandomGenerator()->object();
-    $testCases[] = array($name, $value);
-
-    return $testCases;
-  }
-
-  /**
    * @covers ::createAttributeValue()
-   * @dataProvider createAttributeValueExceptionProvider
    * @expectedException \Exception
    */
-  public function testCreateAttributeValueException($name, $value) {
+  public function testCreateAttributeValueException() {
     $attribute = new Attribute();
+    $name = $this->getRandomGenerator()->string();
+    $value = $this->getRandomGenerator()->object();
     $createAttributeValueMethod = $this->getCreateAttributeValueMethod();
+
     $createAttributeValueMethod->invokeArgs($attribute, array($name, $value));
   }
 
diff --git a/core/themes/engines/twig/twig.engine b/core/themes/engines/twig/twig.engine
index c20da07..bf014bf 100644
--- a/core/themes/engines/twig/twig.engine
+++ b/core/themes/engines/twig/twig.engine
@@ -110,14 +110,17 @@ function twig_render_template($template_file, $variables) {
  * If an array is passed it is rendered via render() and scalar values are
  * returned directly.
  *
+ * @param string $arg_name
+ *   Name of object that will be rendered.
  * @param mixed $arg
  *   String, Object or Render Array
  *
- * @return
- *   The rendered output or an Twig_Markup object.
+ * @return string The rendered output or an Twig_Markup object.
  *
- * @see render
+ * @see render()
  * @see TwigNodeVisitor
+ *
+ * @throws \UnexpectedValueException
  */
 function twig_render_var($arg_name, $arg) {
   // Check for numeric zero.
@@ -144,7 +147,11 @@ function twig_render_var($arg_name, $arg) {
       return (string) $arg;
     }
     else {
-      throw new Exception(t('@arg_name of type "@class" doesn\'t implement __toString.', array('@arg_name' => $arg_name, '@class' => get_class($arg))));
+      throw new \UnexpectedValueException(String::format('@arg_name of type "@class" doesn\'t implement __toString.',
+        array(
+          '@arg_name' => $arg_name,
+          '@class' => get_class($arg),
+        )));
     }
   }