diff --git a/doc/filters/default.rst b/doc/filters/default.rst
index c4ccb56a5..e616e590c 100644
--- a/doc/filters/default.rst
+++ b/doc/filters/default.rst
@@ -21,6 +21,15 @@ undefined:
 .. code-block:: twig
 
     {{ var.method(foo|default('foo'))|default('foo') }}
+    
+Using the ``default`` filter on a boolean variable might trigger unexpected behaviour, as
+``false`` is treated as an empty value. Consider using ``??`` instead:
+
+.. code-block:: twig
+
+    {% set foo = false %}
+    {{ foo|default(true) }} {# true #}
+    {{ foo ?? true }} {# false #}
 
 .. note::
 
diff --git a/src/Environment.php b/src/Environment.php
index 86b517586..4888fad84 100644
--- a/src/Environment.php
+++ b/src/Environment.php
@@ -32,7 +32,7 @@ use Twig\RuntimeLoader\RuntimeLoaderInterface;
 use Twig\TokenParser\TokenParserInterface;
 
 /**
- * Stores the Twig configuration.
+ * Stores the Twig configuration and renders templates.
  *
  * @author Fabien Potencier <fabien@symfony.com>
  */
diff --git a/src/Extension/CoreExtension.php b/src/Extension/CoreExtension.php
index 8bc9c0d63..766d815a8 100644
--- a/src/Extension/CoreExtension.php
+++ b/src/Extension/CoreExtension.php
@@ -563,11 +563,11 @@ function twig_replace_filter($str, $from)
  */
 function twig_round($value, $precision = 0, $method = 'common')
 {
-    if ('common' == $method) {
+    if ('common' === $method) {
         return round($value, $precision);
     }
 
-    if ('ceil' != $method && 'floor' != $method) {
+    if ('ceil' !== $method && 'floor' !== $method) {
         throw new RuntimeError('The round filter only supports the "common", "ceil", and "floor" methods.');
     }
 
@@ -1152,7 +1152,7 @@ function twig_to_array($seq, $preserveKeys = true)
 function twig_test_empty($value)
 {
     if ($value instanceof \Countable) {
-        return 0 == \count($value);
+        return 0 === \count($value);
     }
 
     if ($value instanceof \Traversable) {