diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 681320f99..7650042be 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -12,15 +12,15 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: ['8.2', '8.1', '7.4', '7.3', '7.2', '7.1', '7.0', '5.6']
+        php: ['8.3', '8.1', '8.0', '7.4']
         coverage: [false]
         random: [false]
         include:
-          - php: '8.0'
+          - php: '8.2'
             coverage: true
-          - php: '8.0'
+          - php: '8.2'
             random: true
-          - php: '8.3'
+          - php: '8.4'
             experimental: true
 
     steps:
diff --git a/composer.json b/composer.json
index f8d52ee9a..c7a0ae994 100644
--- a/composer.json
+++ b/composer.json
@@ -4,7 +4,7 @@
   "description": "A collection of AMP tools making it easier to publish and host AMP pages with PHP.",
   "license": "Apache-2.0",
   "require": {
-    "php": "^5.6 || ^7.0 || ^8.0",
+    "php": "^7.4 || ^8.0",
     "ext-dom": "*",
     "ext-filter": "*",
     "ext-iconv": "*",
diff --git a/src/Cli/Executable.php b/src/Cli/Executable.php
index f17da6d00..31b6b0aa2 100644
--- a/src/Cli/Executable.php
+++ b/src/Cli/Executable.php
@@ -77,7 +77,7 @@ abstract class Executable
      * @param Colors|null  $colors    Optional. Instance of the Colors object to use. Defaults to null to instantiate a
      *                                new one.
      */
-    public function __construct($autocatch = true, Options $options = null, Colors $colors = null)
+    public function __construct($autocatch = true, ?Options $options = null, ?Colors $colors = null)
     {
         if ($autocatch) {
             set_exception_handler([$this, 'fatal']);
diff --git a/src/Cli/Options.php b/src/Cli/Options.php
index ec2051d4d..8b7821119 100644
--- a/src/Cli/Options.php
+++ b/src/Cli/Options.php
@@ -77,7 +77,7 @@ class Options
      * @param Colors $colors Optional. Configured color object.
      * @throws InvalidArgument When arguments can't be read.
      */
-    public function __construct(Colors $colors = null)
+    public function __construct(?Colors $colors = null)
     {
         $this->colors = $colors instanceof Colors ? $colors : new Colors();
 
diff --git a/src/Cli/TableFormatter.php b/src/Cli/TableFormatter.php
index 49a7960c6..6ed660465 100644
--- a/src/Cli/TableFormatter.php
+++ b/src/Cli/TableFormatter.php
@@ -74,7 +74,7 @@ class TableFormatter
      *
      * @param Colors|null $colors Optional. Instance of the Colors helper object.
      */
-    public function __construct(Colors $colors = null)
+    public function __construct(?Colors $colors = null)
     {
         // Try to get terminal width.
         $width = $this->getTerminalWidth();
diff --git a/src/CssLength.php b/src/CssLength.php
index a4b3821c8..0af3fe269 100644
--- a/src/CssLength.php
+++ b/src/CssLength.php
@@ -112,7 +112,7 @@ public function validate($allowAuto, $allowFluid)
         if (preg_match($pattern, $this->attrValue, $match)) {
             $this->isValid = true;
             $this->numeral = isset($match['numeral']) ? (float)$match['numeral'] : $this->numeral;
-            $this->unit    = isset($match['unit']) ? $match['unit'] : $this->unit;
+            $this->unit    = $match['unit'] ?? $this->unit;
         }
     }
 
diff --git a/src/Dom/Document.php b/src/Dom/Document.php
index 4f0a46fcf..f9a7a6a38 100644
--- a/src/Dom/Document.php
+++ b/src/Dom/Document.php
@@ -227,7 +227,7 @@ public static function fromHtml($html, $options = [])
             $options = [Option::ENCODING => $options];
         }
 
-        $encoding = isset($options[Option::ENCODING]) ? $options[Option::ENCODING] : null;
+        $encoding = $options[ Option::ENCODING ] ?? null;
 
         $dom = new self('', $encoding);
 
@@ -258,7 +258,7 @@ public static function fromHtmlFragment($html, $options = [])
             $options = [Option::ENCODING => $options];
         }
 
-        $encoding = isset($options[Option::ENCODING]) ? $options[Option::ENCODING] : null;
+        $encoding = $options[ Option::ENCODING ] ?? null;
 
         $dom = new self('', $encoding);
 
@@ -413,7 +413,7 @@ public function loadHTMLFragment($source, $options = [])
      * @return string The HTML, or false if an error occurred.
      */
     #[\ReturnTypeWillChange]
-    public function saveHTML(DOMNode $node = null)
+    public function saveHTML(?DOMNode $node = null)
     {
         return $this->saveHTMLFragment($node);
     }
@@ -424,7 +424,7 @@ public function saveHTML(DOMNode $node = null)
      * @param DOMNode|null $node Optional. Parameter to output a subset of the document.
      * @return string The HTML fragment, or false if an error occurred.
      */
-    public function saveHTMLFragment(DOMNode $node = null)
+    public function saveHTMLFragment(?DOMNode $node = null)
     {
         $filtersInReverse = array_reverse($this->filters);
 
@@ -551,7 +551,7 @@ private function normalizeDocumentStructure($content)
             $content   = preg_replace(self::HTML_STRUCTURE_HTML_START_TAG, '', $content, 1);
 
             preg_match(self::HTML_STRUCTURE_HTML_END_TAG, $content, $matches);
-            $htmlEnd = isset($matches['html_end']) ? $matches['html_end'] : $htmlEnd;
+            $htmlEnd = $matches['html_end'] ?? $htmlEnd;
             $content = preg_replace(self::HTML_STRUCTURE_HTML_END_TAG, '', $content, 1);
         }
 
diff --git a/src/Dom/Document/Filter/AmpBindAttributes.php b/src/Dom/Document/Filter/AmpBindAttributes.php
index 73ce896ae..7a5ffd2d3 100644
--- a/src/Dom/Document/Filter/AmpBindAttributes.php
+++ b/src/Dom/Document/Filter/AmpBindAttributes.php
@@ -215,7 +215,7 @@ public function afterSave($html)
                     ||
                     in_array($attrName, $this->convertedAmpBindAttributes, true)
                 ) {
-                    $attrValue = isset($attrMatches['value']) ? $attrMatches['value'] : '=""';
+                    $attrValue = $attrMatches['value'] ?? '=""';
                     $newAttrs .= " [{$attrName}]{$attrValue}";
                 } else {
                     $newAttrs .= $attrMatches[0];
diff --git a/src/Dom/Options.php b/src/Dom/Options.php
index 522337ef2..7bf611b54 100644
--- a/src/Dom/Options.php
+++ b/src/Dom/Options.php
@@ -72,7 +72,7 @@ public function offsetUnset($option)
     #[\ReturnTypeWillChange]
     public function offsetGet($option)
     {
-        return isset($this->options[$option]) ? $this->options[$option] : null;
+        return $this->options[ $option ] ?? null;
     }
 
     /**
diff --git a/src/Optimizer/Error/CannotPreloadImage.php b/src/Optimizer/Error/CannotPreloadImage.php
index e6d5058ec..e1df4fc33 100644
--- a/src/Optimizer/Error/CannotPreloadImage.php
+++ b/src/Optimizer/Error/CannotPreloadImage.php
@@ -25,7 +25,7 @@ final class CannotPreloadImage implements Error
      * @param Element|null $element Optional. Image element that has the srcset attribute, or null if no element.
      * @return self
      */
-    public static function fromImageWithSrcsetAttribute(Element $element = null)
+    public static function fromImageWithSrcsetAttribute(?Element $element = null)
     {
         $message = self::SRCSET_STRING;
 
diff --git a/src/Optimizer/TransformationEngine.php b/src/Optimizer/TransformationEngine.php
index 512aab7c1..192470a86 100644
--- a/src/Optimizer/TransformationEngine.php
+++ b/src/Optimizer/TransformationEngine.php
@@ -51,14 +51,14 @@ final class TransformationEngine
      * @param Configuration|null    $configuration Optional. Configuration data to use for setting up the transformers.
      * @param RemoteGetRequest|null $remoteRequest Optional. Transport to use for remote requests. Defaults to the
      *                                             CurlRemoteGetRequest implementation shipped with the library.
-     * @param Spec                  $spec          Optional. Validator spec instance to use.
+     * @param Spec|null             $spec          Optional. Validator spec instance to use.
      */
     public function __construct(
-        Configuration $configuration = null,
-        RemoteGetRequest $remoteRequest = null,
-        Spec $spec = null
+        ?Configuration $configuration = null,
+        ?RemoteGetRequest $remoteRequest = null,
+        ?Spec $spec = null
     ) {
-        $this->configuration = isset($configuration) ? $configuration : new DefaultConfiguration();
+        $this->configuration = $configuration ?? new DefaultConfiguration();
         $this->remoteRequest = $remoteRequest;
         $this->spec          = $spec;
 
diff --git a/src/Url.php b/src/Url.php
index 0b30c09b3..76228c6be 100644
--- a/src/Url.php
+++ b/src/Url.php
@@ -138,7 +138,7 @@ final class Url
      * @param Url|null    $baseUrl Base URL.
      * @throws FailedToParseUrl Exception when the URL or Base URL is malformed.
      */
-    public function __construct($url = null, Url $baseUrl = null)
+    public function __construct($url = null, ?Url $baseUrl = null)
     {
         $parsedUrl = [];
 
diff --git a/src/Validator/ValidationHandler.php b/src/Validator/ValidationHandler.php
index 339c635d2..1a098f570 100644
--- a/src/Validator/ValidationHandler.php
+++ b/src/Validator/ValidationHandler.php
@@ -56,7 +56,7 @@ final class ValidationHandler implements HtmlSaxHandlerWithLocation
      */
     private $validationResult;
 
-    public function __construct($htmlFormat = Format::AMP, Spec $spec = null)
+    public function __construct($htmlFormat = Format::AMP, ?Spec $spec = null)
     {
         $this->htmlFormat       = $htmlFormat;
         $this->spec             = $spec instanceof Spec ? $spec : new Spec();
diff --git a/src/Validator/ValidationResult.php b/src/Validator/ValidationResult.php
index d301ae2ea..96313c4e4 100644
--- a/src/Validator/ValidationResult.php
+++ b/src/Validator/ValidationResult.php
@@ -85,8 +85,8 @@ final class ValidationResult
      *                                                        array.
      */
     public function __construct(
-        ValidationStatus $status = null,
-        ValidationErrorCollection $errors = null,
+        ?ValidationStatus $status = null,
+        ?ValidationErrorCollection $errors = null,
         $specRevision = -1,
         $transformerVersion = 0,
         $typeIdentifiers = [],
diff --git a/src/Validator/ValidatorRules.php b/src/Validator/ValidatorRules.php
index 1ad0a507d..2cc8aeb90 100644
--- a/src/Validator/ValidatorRules.php
+++ b/src/Validator/ValidatorRules.php
@@ -72,7 +72,7 @@ final class ValidatorRules
      * @param string    $htmlFormat Optional. AMP HTML format to validate against.
      * @param Spec|null $spec       Optional. Validator specification to use.
      */
-    public function __construct($htmlFormat = Format::AMP, Spec $spec = null)
+    public function __construct($htmlFormat = Format::AMP, ?Spec $spec = null)
     {
         $this->htmlFormat = $htmlFormat;
         $this->spec       = $spec instanceof Spec ? $spec : new Spec();
diff --git a/tests/Optimizer/TransformationEngineTest.php b/tests/Optimizer/TransformationEngineTest.php
index 3b8ae3f43..a0d2237d6 100644
--- a/tests/Optimizer/TransformationEngineTest.php
+++ b/tests/Optimizer/TransformationEngineTest.php
@@ -132,7 +132,7 @@ public function testDependencyResolution($transformerClass)
      * @param Configuration|null $configuration Optional. Configuration object to use.
      * @return TransformationEngine Transformation engine instance to test against.
      */
-    private function getTransformationEngine(Configuration $configuration = null)
+    private function getTransformationEngine(?Configuration $configuration = null)
     {
         return new TransformationEngine(
             $configuration,