diff --git a/src/widgets/navigation/NavBar.php b/src/widgets/navigation/NavBar.php
index d681daf..8b1ce58 100644
--- a/src/widgets/navigation/NavBar.php
+++ b/src/widgets/navigation/NavBar.php
@@ -213,6 +213,11 @@ public function run()
         return implode("\n", $html);
     }
 
+    /**
+     * Initializes the side nav options.
+     *
+     * @param string $sidenavId the side nav element's HTML id attribute.
+     */
     protected function initSidenav($sidenavId)
     {
         $this->sidenavToggleButtonOptions = ArrayHelper::merge([
@@ -246,6 +251,12 @@ protected function renderSidenav($sidenavId)
         ]);
     }
 
+    /**
+     * Renders the side nav toggle button.
+     *
+     * @return string the button markup.
+     * @throws \Exception
+     */
     protected function renderSidenavToggleButton()
     {
         return Button::widget($this->sidenavToggleButtonOptions);
diff --git a/src/widgets/navigation/SideNav.php b/src/widgets/navigation/SideNav.php
index 656c25f..42ff373 100644
--- a/src/widgets/navigation/SideNav.php
+++ b/src/widgets/navigation/SideNav.php
@@ -66,7 +66,6 @@ class SideNav extends Nav
      * @var array the configuration options for the toggle button.
      * The toggle button is rendered by the [[Button]] widget. See the docs for all available options.
      *
-     *
      * @see Button|Button
      */
     public $toggleButtonOptions = [];
@@ -184,6 +183,16 @@ protected function renderItem($item)
         return Html::tag('li', $content, $listItemOptions);
     }
 
+    /**
+     * Renders a submenu as Collapsible in side navigation element.
+     *
+     * @param string $link the trigger link.
+     * @param array $items the submenu items.
+     * @param bool $isParentActive whether the submenu's parent list element shall get an 'active' state.
+     * @return string the Collapsible markup.
+     *
+     * @throws \Exception
+     */
     protected function renderCollapsible($link, $items = [], $isParentActive = false)
     {
         $itemOptions = [];
@@ -205,7 +214,13 @@ protected function renderCollapsible($link, $items = [], $isParentActive = false
         ]);
     }
 
-    protected function buildCollapsibleBody($items)
+    /**
+     * Build the needed markup for the collapsible body, i. e. the `<ul>` containing the submenu links.
+     *
+     * @param array $items the submenu items.
+     * @return string the Collapsible body markup.
+     */
+    protected function buildCollapsibleBody($items = [])
     {
         $html[] = Html::beginTag('ul');