diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
index 1f67586..ce25af1 100644
--- a/.github/workflows/continuous-integration.yml
+++ b/.github/workflows/continuous-integration.yml
@@ -26,9 +26,11 @@ jobs:
           - '8.0'
           - '8.1'
           - '8.2'
+          - '8.3'
+          - '8.4'
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        uses: actions/checkout@v4
 
       - name: Setup PHP ${{ matrix.php-version }}
         uses: shivammathur/setup-php@v2
@@ -43,7 +45,7 @@ jobs:
         run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Cache dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
@@ -56,6 +58,39 @@ jobs:
         run: php -d xdebug.mode=coverage ./vendor/bin/phpunit --coverage-clover=coverage.xml
 
       - name: Upload coverage report
-        uses: codecov/codecov-action@v2
+        uses: codecov/codecov-action@v3
         with:
           fail_ci_if_error: false
+
+  static-analysis:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup PHP 8.4
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.4'
+          tools: composer:2.2
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+
+      - name: Cache dependencies
+        uses: actions/cache@v4
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Install dependencies
+        run: composer install --no-interaction --prefer-dist
+
+      - name: Install PHPStan
+        run: composer require --dev phpstan/phpstan --with-all-dependencies
+
+      - name: Run PHPStan
+        run: composer phpstan
diff --git a/composer.json b/composer.json
index 16138d5..2693864 100644
--- a/composer.json
+++ b/composer.json
@@ -41,6 +41,11 @@
     "require-dev": {
         "yoast/phpunit-polyfills": "~1.0"
     },
+    "scripts": {
+        "phpstan": "phpstan analyse --level=2 src/",
+        "test": "./vendor/bin/phpunit",
+        "test-coverage": "php -d xdebug.mode=coverage ./vendor/bin/phpunit --coverage-clover=coverage.xml"
+    },
     "autoload-dev": {
         "psr-4": {
             "Aura\\Html\\": "tests/",
diff --git a/src/Escaper.php b/src/Escaper.php
index 845a83c..31c7ed1 100644
--- a/src/Escaper.php
+++ b/src/Escaper.php
@@ -124,7 +124,7 @@ public function __invoke()
      *
      * @param string $encoding The encoding to use.
      *
-     * @return null
+     * @return void
      *
      */
     public function setEncoding($encoding)
@@ -141,7 +141,7 @@ public function setEncoding($encoding)
      *
      * @param int $flags The `htmlspecialchars()` flags.
      *
-     * @return null
+     * @return void
      *
      */
     public function setFlags($flags)
@@ -212,7 +212,7 @@ public function js($raw)
      *
      * @param Escaper $escaper The Escaper to use as the singleton.
      *
-     * @return null
+     * @return void
      *
      */
     public static function setStatic(Escaper $escaper)
diff --git a/src/Escaper/AbstractEscaper.php b/src/Escaper/AbstractEscaper.php
index ddc760a..4566cff 100644
--- a/src/Escaper/AbstractEscaper.php
+++ b/src/Escaper/AbstractEscaper.php
@@ -78,7 +78,7 @@ abstract public function __invoke($raw);
      *
      * @param string $encoding The encoding.
      *
-     * @return null
+     * @return void
      *
      */
     public function setEncoding($encoding)
diff --git a/src/Escaper/HtmlEscaper.php b/src/Escaper/HtmlEscaper.php
index c05e98e..8a151c9 100644
--- a/src/Escaper/HtmlEscaper.php
+++ b/src/Escaper/HtmlEscaper.php
@@ -85,7 +85,7 @@ public function __invoke($raw)
      *
      * @param int $flags The flags for `htmlspecialchars()`.
      *
-     * @return null
+     * @return void
      *
      */
     public function setFlags($flags)
diff --git a/src/EscaperFactory.php b/src/EscaperFactory.php
index 47cc7b9..fdad362 100644
--- a/src/EscaperFactory.php
+++ b/src/EscaperFactory.php
@@ -60,10 +60,6 @@ public function __construct($encoding = null, $flags = null)
      *
      * Creates a new Escaper object.
      *
-     * @param string $encoding The encoding for the escapers.
-     *
-     * @param int $flags The `htmlspecialchars()` flags for the escapers.
-     *
      * @return Escaper
      *
      */
diff --git a/src/Helper/AbstractHelper.php b/src/Helper/AbstractHelper.php
index 82f9476..61f0f1a 100644
--- a/src/Helper/AbstractHelper.php
+++ b/src/Helper/AbstractHelper.php
@@ -66,7 +66,7 @@ public function __construct(Escaper $escaper)
      *
      * @param string $indent The indent string.
      *
-     * @return null
+     * @return void
      *
      */
     public function setIndent($indent)
diff --git a/src/Helper/AbstractList.php b/src/Helper/AbstractList.php
index cadf680..3b569e8 100644
--- a/src/Helper/AbstractList.php
+++ b/src/Helper/AbstractList.php
@@ -21,7 +21,7 @@ abstract class AbstractList extends AbstractHelper
      *
      * Attributes for the ul tag.
      *
-     * @var array
+     * @var array<string, scalar|null>
      *
      */
     protected $attr = array();
@@ -30,7 +30,7 @@ abstract class AbstractList extends AbstractHelper
      *
      * The stack of HTML elements.
      *
-     * @var array
+     * @var array<int, array{string, string}>
      *
      */
     protected $stack = array();
@@ -46,14 +46,13 @@ abstract class AbstractList extends AbstractHelper
 
     /**
      *
-     * Initializes and returns the UL object.
+     * Initializes and returns the list object.
      *
-     * @param array $attr Attributes for the UL tag.
+     * @param array<string, scalar|null>|null $attr HTML element attributes
      *
      * @return self
-     *
      */
-    public function __invoke(array $attr = null)
+    public function __invoke($attr = null)
     {
         if ($attr !== null) {
             $this->attr = $attr;
@@ -187,7 +186,7 @@ public function rawItems(array $items)
      *
      * @param string $item The item HTML.
      *
-     * @return null
+     * @return void
      *
      */
     protected function buildItem($item)
diff --git a/src/Helper/AbstractSeries.php b/src/Helper/AbstractSeries.php
index 360985f..23c27a7 100644
--- a/src/Helper/AbstractSeries.php
+++ b/src/Helper/AbstractSeries.php
@@ -73,7 +73,7 @@ public function __toString()
      *
      * @param string $element The element itself.
      *
-     * @return null
+     * @return void
      *
      */
     protected function addElement($pos, $element)
diff --git a/src/Helper/Input.php b/src/Helper/Input.php
index bb659a7..5ff077e 100644
--- a/src/Helper/Input.php
+++ b/src/Helper/Input.php
@@ -23,12 +23,11 @@ class Input extends HelperLocator
      *
      * Given an input specification, returns the HTML for the input.
      *
-     * @param array $spec The element specification.
-     *
-     * @return mixed
+     * @param array{type?: string, name?: string, attribs?: array<string, scalar|null>, value?: mixed, options?: array<string, string>}|null $spec HTML input element specification
      *
+     * @return self|string
      */
-    public function __invoke(array $spec = null)
+    public function __invoke($spec = null)
     {
         if ($spec === null) {
             return $this;
diff --git a/src/Helper/Input/AbstractChecked.php b/src/Helper/Input/AbstractChecked.php
index 7c933a0..517a155 100644
--- a/src/Helper/Input/AbstractChecked.php
+++ b/src/Helper/Input/AbstractChecked.php
@@ -68,7 +68,7 @@ protected function htmlChecked()
      *
      * Extracts and retains the "label" pseudo-attribute.
      *
-     * @return null
+     * @return void
      *
      */
     protected function setLabel()
@@ -86,7 +86,7 @@ protected function setLabel()
      *
      * Sets the "checked" attribute appropriately.
      *
-     * @return null
+     * @return void
      *
      */
     protected function setChecked()
diff --git a/src/Helper/Input/AbstractInput.php b/src/Helper/Input/AbstractInput.php
index ce5cb8c..3beceaa 100644
--- a/src/Helper/Input/AbstractInput.php
+++ b/src/Helper/Input/AbstractInput.php
@@ -25,6 +25,7 @@ abstract class AbstractInput extends AbstractHelper
      * The input type.
      *
      * @var string
+     * @readonly
      *
      */
     protected $type;
@@ -51,7 +52,7 @@ abstract class AbstractInput extends AbstractHelper
      *
      * HTML attributes for the input.
      *
-     * @var array
+     * @var array<string, scalar|null>
      *
      */
     protected $attribs = array();
@@ -60,21 +61,20 @@ abstract class AbstractInput extends AbstractHelper
      *
      * Value options for the input.
      *
-     * @var array
+     * @var array<string, string>
      *
      */
     protected $options = array();
 
     /**
      *
-     * Given a input spec, returns the HTML for the input.
+     * Returns the input helper with optional specification.
      *
-     * @param array $spec The input spec.
-     *
-     * @return string
+     * @param array{type?: string, name?: string, attribs?: array<string, scalar|null>, value?: mixed, options?: array<string, string>}|null $spec HTML input element specification
      *
+     * @return self
      */
-    public function __invoke(array $spec = null)
+    public function __invoke($spec = null)
     {
         if ($spec !== null) {
             $this->prep($spec);
diff --git a/src/Helper/Input/Select.php b/src/Helper/Input/Select.php
index 7896ff5..c5d80ac 100644
--- a/src/Helper/Input/Select.php
+++ b/src/Helper/Input/Select.php
@@ -72,7 +72,7 @@ class Select extends AbstractInput
      * @return string|self
      *
      */
-    public function __invoke(array $spec = null)
+    public function __invoke($spec = null)
     {
         if ($spec !== null) {
             $this->prep($spec);
@@ -291,6 +291,7 @@ protected function buildOptionPlaceholder()
                 array('disabled' => true),
             ));
         }
+        return '';
     }
 
     /**
diff --git a/src/Helper/Scripts.php b/src/Helper/Scripts.php
index 2282049..d024e78 100644
--- a/src/Helper/Scripts.php
+++ b/src/Helper/Scripts.php
@@ -57,7 +57,7 @@ public function add($src, $pos = 100, array $attr = array())
      *
      * @param string $src The source href for the script.
      *
-     * @param string $pos The script position in the stack.
+     * @param int $pos The script position in the stack.
      *
      * @param array $attr The additional attributes
      *
@@ -122,7 +122,7 @@ public function addCondInternal($cond, $script, $pos = 100, array $attr = array(
      * @param array $attr The additional attributes
      *
      *
-     * @return null
+     * @return void
      *
      * @access public
      */
@@ -139,7 +139,7 @@ public function beginInternal($pos = 100, array $attr = array())
      * @param int   $pos  position
      * @param array $attr The additional attributes
      *
-     * @return null
+     * @return void
      *
      * @access public
      */
diff --git a/src/Helper/Styles.php b/src/Helper/Styles.php
index 510d91c..cdb4b88 100644
--- a/src/Helper/Styles.php
+++ b/src/Helper/Styles.php
@@ -18,9 +18,10 @@
 class Styles extends AbstractSeries
 {
     /**
-     * Temporary storage or params passed to caputre functions
+     * Temporary storage for capture functions
      *
-     * @var mixed
+     * @var array<int, array{attr: mixed, pos: int, cond?: string}>
+     * @readonly
      *
      * @access private
      */
@@ -28,18 +29,17 @@ class Styles extends AbstractSeries
 
     /**
      *
-     * Adds a <link rel="stylesheet" ... /> tag to the series.
+     * Adds a stylesheet link to the series.
      *
-     * @param string $href The source href for the stylesheet.
+     * @param string $href CSS file URL or path
      *
-     * @param array $attr Additional attributes for the <link> tag.
+     * @param array<string, scalar|null>|null $attr Additional HTML attributes
      *
-     * @param int $pos The stylesheet position in the series.
+     * @param int $pos Position in the output series
      *
      * @return self
-     *
      */
-    public function add($href, array $attr = null, $pos = 100)
+    public function add($href, $attr = null, $pos = 100)
     {
         $attr = $this->fixAttr($href, $attr);
         $tag = $this->void('link', $attr);
@@ -50,21 +50,19 @@ public function add($href, array $attr = null, $pos = 100)
 
     /**
      *
-     * Adds a conditional `<!--[if ...]><link rel="stylesheet" ... /><![endif] -->`
-     * tag to the stack.
+     * Adds a conditional stylesheet link.
      *
-     * @param string $cond The conditional expression for the stylesheet.
+     * @param string $cond IE conditional expression
      *
-     * @param string $href The source href for the stylesheet.
+     * @param string $href CSS file URL or path
      *
-     * @param array $attr Additional attributes for the <link> tag.
+     * @param array<string, scalar|null>|null $attr Additional HTML attributes
      *
-     * @param string $pos The stylesheet position in the stack.
+     * @param int $pos Position in the output series
      *
      * @return self
-     *
      */
-    public function addCond($cond, $href, array $attr = null, $pos = 100)
+    public function addCond($cond, $href, $attr = null, $pos = 100)
     {
         $attr = $this->fixAttr($href, $attr);
         $link = $this->void('link', $attr);
@@ -85,7 +83,7 @@ public function addCond($cond, $href, array $attr = null, $pos = 100)
      *
      * @access protected
      */
-    protected function style($css, array $attr = null)
+    protected function style($css, $attr = null)
     {
         $attr = $this->fixInternalAttr($attr);
         $attr = $this->escaper->attr($attr);
@@ -103,7 +101,7 @@ protected function style($css, array $attr = null)
      *
      * @access public
      */
-    public function addInternal($css, array $attr = null, $pos = 100)
+    public function addInternal($css, $attr = null, $pos = 100)
     {
         $style = $this->style($css, $attr);
         $this->addElement($pos, $style);
@@ -121,12 +119,12 @@ public function addInternal($css, array $attr = null, $pos = 100)
      *
      * @param array $attr Additional attributes for the <style> tag.
      *
-     * @param string $pos The position in the stack.
+     * @param int $pos The position in the stack.
      *
      * @return self
      *
      */
-    public function addCondInternal($cond, $css, array $attr = null, $pos = 100)
+    public function addCondInternal($cond, $css, $attr = null, $pos = 100)
     {
         $style = $this->style($css, $attr);
         $cond  = $this->escaper->html($cond);
@@ -146,7 +144,7 @@ public function addCondInternal($cond, $css, array $attr = null, $pos = 100)
      *
      * @access public
      */
-    public function beginInternal(array $attr = null, $pos = 100)
+    public function beginInternal($attr = null, $pos = 100)
     {
         $this->capture[] = array(
             'attr' => $attr,
@@ -167,7 +165,7 @@ public function beginInternal(array $attr = null, $pos = 100)
      *
      * @access public
      */
-    public function beginCondInternal($cond, array $attr = null, $pos = 100)
+    public function beginCondInternal($cond, $attr = null, $pos = 100)
     {
         $this->capture[] = array(
             'attr' => $attr,
@@ -215,7 +213,7 @@ public function endInternal()
      *
      * @access protected
      */
-    protected function fixInternalAttr(array $attr = null)
+    protected function fixInternalAttr($attr = null)
     {
         $attr = (array) $attr;
 
@@ -241,7 +239,7 @@ protected function fixInternalAttr(array $attr = null)
      * @return array The fixed attributes.
      *
      */
-    protected function fixAttr($href, array $attr = null)
+    protected function fixAttr($href, $attr = null)
     {
         $attr = (array) $attr;
 
diff --git a/src/HelperLocator.php b/src/HelperLocator.php
index 9154d90..33278eb 100644
--- a/src/HelperLocator.php
+++ b/src/HelperLocator.php
@@ -75,7 +75,7 @@ public function __call($name, $args)
      *
      * @param callable $callable A callable to create the helper object.
      *
-     * @return null
+     * @return void
      *
      */
     public function set($name, $callable)