diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 08c0b0a2d..2a7e69fb7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,19 +12,22 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-versions: ['8.0', '8.1', '8.2', '8.3', '8.4']
+        php-versions: ['8.3', '8.4']
         coverage: ['pcov']
         code-style: ['no']
         code-analysis: ['no']
+        rector-check: ['no']
         include:
-          - php-versions: '7.4'
+          - php-versions: '8.2'
             coverage: 'pcov'
             code-style: 'yes'
             code-analysis: 'yes'
+            rector-check: 'no'
           - php-versions: '8.5'
             coverage: 'pcov'
             code-style: 'no'
             code-analysis: 'yes'
+            rector-check: 'yes'
     steps:
       - name: Checkout
         uses: actions/checkout@v6
@@ -61,6 +64,10 @@ jobs:
         if: matrix.code-analysis == 'yes'
         run: composer phpstan
 
+      - name: Code Refactoring (rector)
+        if: matrix.rector-check == 'yes'
+        run: composer rector-check
+
       - name: Test with phpunit
         run: vendor/bin/phpunit --configuration tests/phpunit.xml --coverage-clover clover.xml
 
diff --git a/.gitignore b/.gitignore
index d0e5169ac..f38607123 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@ vendor/
 composer.lock
 tests/cov/
 tests/temp
+tests/.phpunit.cache
 tests/.phpunit.result.cache
 
 # Development stuff
diff --git a/composer.json b/composer.json
index 561906176..8ae9f914a 100644
--- a/composer.json
+++ b/composer.json
@@ -32,16 +32,20 @@
     "homepage" : "http://sabre.io/vobject/",
     "license" : "BSD-3-Clause",
     "require" : {
-        "php"          : "^7.4 || ^8.0",
+        "php"          : "^8.2",
         "ext-mbstring" : "*",
         "ext-json"     : "*",
         "sabre/xml"    : "^3.0 || ^4.0"
     },
     "require-dev" : {
-        "friendsofphp/php-cs-fixer": "^3.94",
-        "phpunit/phpunit" : "^9.6",
-        "phpunit/php-invoker" : "^2.0 || ^3.1",
-        "phpstan/phpstan": "^2.1"
+        "friendsofphp/php-cs-fixer": "^3.95",
+        "phpstan/phpstan": "^2.2",
+        "phpstan/phpstan-phpunit": "^2.0",
+        "phpstan/phpstan-strict-rules": "^2.0",
+        "phpstan/extension-installer": "^1.4",
+        "phpunit/phpunit": "^11.5",
+        "phpunit/php-invoker" : "^5.0",
+        "rector/rector": "^2.4"
     },
     "suggest" : {
         "hoa/bench"       : "If you would like to run the benchmark scripts"
@@ -96,6 +100,12 @@
         "cs-fixer": [
             "PHP_CS_FIXER_IGNORE_ENV=true php-cs-fixer fix"
         ],
+        "rector-check": [
+            "rector process --dry-run"
+        ],
+        "rector-fix": [
+            "rector process"
+        ],
         "phpunit": [
             "phpunit --configuration tests/phpunit.xml"
         ],
@@ -104,5 +114,13 @@
             "composer cs-fixer",
             "composer phpunit"
         ]
+    },
+    "config": {
+        "allow-plugins": {
+            "phpstan/extension-installer": true
+        },
+        "platform": {
+            "php": "8.2"
+        }
     }
 }
diff --git a/lib/BirthdayCalendarGenerator.php b/lib/BirthdayCalendarGenerator.php
index 49793b0d4..11ae8be14 100644
--- a/lib/BirthdayCalendarGenerator.php
+++ b/lib/BirthdayCalendarGenerator.php
@@ -95,7 +95,7 @@ public function getResult(): VCalendar
             // We've seen clients (ez-vcard) putting "BDAY:" properties
             // without a value into vCards. If we come across those, we'll
             // skip them.
-            if (empty($object->BDAY->getValue())) {
+            if ('' === $object->BDAY->getValue()) {
                 continue;
             }
 
@@ -116,7 +116,7 @@ public function getResult(): VCalendar
             // Skip if we can't parse the BDAY value.
             try {
                 $dateParts = DateTimeParser::parseVCardDateTime($object->BDAY->getValue());
-            } catch (InvalidDataException $e) {
+            } catch (InvalidDataException) {
                 continue;
             }
 
diff --git a/lib/Cli.php b/lib/Cli.php
index 69af6f470..386cf2c73 100644
--- a/lib/Cli.php
+++ b/lib/Cli.php
@@ -92,7 +92,7 @@ public function main(array $argv): int
         // @codeCoverageIgnoreEnd
 
         try {
-            list($options, $positional) = $this->parseArguments($argv);
+            [$options, $positional] = $this->parseArguments($argv);
 
             if (isset($options['q'])) {
                 $this->quiet = true;
@@ -110,27 +110,10 @@ public function main(array $argv): int
 
                         return 0;
                     case 'format':
-                        switch ($value) {
-                            // jcard/jcal documents
-                            case 'jcard':
-                            case 'jcal':
-                                // specific document versions
-                            case 'vcard21':
-                            case 'vcard30':
-                            case 'vcard40':
-                            case 'icalendar20':
-                                // specific formats
-                            case 'json':
-                            case 'mimedir':
-                                // icalendar/vcard
-                            case 'icalendar':
-                            case 'vcard':
-                                $this->format = $value;
-                                break;
-
-                            default:
-                                throw new \InvalidArgumentException('Unknown format: '.$value);
-                        }
+                        $this->format = match ($value) {
+                            'jcard', 'jcal', 'vcard21', 'vcard30', 'vcard40', 'icalendar20', 'json', 'mimedir', 'icalendar', 'vcard' => $value,
+                            default => throw new \InvalidArgumentException('Unknown format: '.$value),
+                        };
                         break;
                     case 'pretty':
                         $this->pretty = true;
@@ -139,28 +122,11 @@ public function main(array $argv): int
                         $this->forgiving = true;
                         break;
                     case 'inputformat':
-                        switch ($value) {
-                            // json formats
-                            case 'jcard':
-                            case 'jcal':
-                            case 'json':
-                                $this->inputFormat = 'json';
-                                break;
-
-                                // mimedir formats
-                            case 'mimedir':
-                            case 'icalendar':
-                            case 'vcard':
-                            case 'vcard21':
-                            case 'vcard30':
-                            case 'vcard40':
-                            case 'icalendar20':
-                                $this->inputFormat = 'mimedir';
-                                break;
-
-                            default:
-                                throw new \InvalidArgumentException('Unknown format: '.$value);
-                        }
+                        $this->inputFormat = match ($value) {
+                            'jcard', 'jcal', 'json' => 'json',
+                            'mimedir', 'icalendar', 'vcard', 'vcard21', 'vcard30', 'vcard40', 'icalendar20' => 'mimedir',
+                            default => throw new \InvalidArgumentException('Unknown format: '.$value),
+                        };
                         break;
                     default:
                         throw new \InvalidArgumentException('Unknown option: '.$name);
@@ -181,7 +147,7 @@ public function main(array $argv): int
                 throw new \InvalidArgumentException('Too many arguments');
             }
 
-            if (!in_array($positional[0], ['validate', 'repair', 'convert', 'color'])) {
+            if (!in_array($positional[0], ['validate', 'repair', 'convert', 'color'], true)) {
                 throw new \InvalidArgumentException('Unknown command: '.$positional[0]);
             }
         } catch (\InvalidArgumentException $e) {
@@ -201,14 +167,14 @@ public function main(array $argv): int
         }
 
         if (null === $this->inputFormat) {
-            if ('.json' === substr($this->inputPath, -5)) {
+            if (str_ends_with($this->inputPath, '.json')) {
                 $this->inputFormat = 'json';
             } else {
                 $this->inputFormat = 'mimedir';
             }
         }
         if (null === $this->format) {
-            if ('.json' === substr($this->outputPath, -5)) {
+            if (str_ends_with($this->outputPath, '.json')) {
                 $this->format = 'json';
             } else {
                 $this->format = 'mimedir';
@@ -219,12 +185,13 @@ public function main(array $argv): int
 
         try {
             while ($input = $this->readInput()) {
+                // @phpstan-ignore method.dynamicName
                 $returnCode = $this->$command($input);
                 if (0 !== $returnCode) {
                     $realCode = $returnCode;
                 }
             }
-        } catch (EofException $e) {
+        } catch (EofException) {
             // end of file
         } catch (\Exception $e) {
             $this->log('Error: '.$e->getMessage(), 'red');
@@ -408,7 +375,7 @@ protected function convert(Component $vObj): int
             }
             fwrite($this->stdout, json_encode($vObj->jsonSerialize(), $jsonOptions));
         } else {
-            fwrite($this->stdout, $vObj->serialize());
+            fwrite($this->stdout, (string) $vObj->serialize());
         }
 
         return 0;
@@ -538,7 +505,7 @@ protected function serializeProperty(Property $property): void
         $this->cWrite('red', ':');
 
         if ($property instanceof Property\Binary) {
-            $this->cWrite('default', 'embedded binary stripped. ('.strlen($property->getValue()).' bytes)');
+            $this->cWrite('default', 'embedded binary stripped. ('.strlen((string) $property->getValue()).' bytes)');
         } else {
             $parts = $property->getParts();
             $first1 = true;
@@ -593,17 +560,17 @@ protected function parseArguments(array $argv): array
 
             $v = $argv[$ii];
 
-            if ('--' === substr($v, 0, 2)) {
+            if (str_starts_with((string) $v, '--')) {
                 // This is a long-form option.
-                $optionName = substr($v, 2);
+                $optionName = substr((string) $v, 2);
                 $optionValue = true;
                 if (strpos($optionName, '=')) {
-                    list($optionName, $optionValue) = explode('=', $optionName);
+                    [$optionName, $optionValue] = explode('=', $optionName);
                 }
                 $options[$optionName] = $optionValue;
-            } elseif ('-' === substr($v, 0, 1) && strlen($v) > 1) {
+            } elseif (str_starts_with((string) $v, '-') && strlen((string) $v) > 1) {
                 // This is a short-form option.
-                foreach (str_split(substr($v, 1)) as $option) {
+                foreach (str_split(substr((string) $v, 1)) as $option) {
                     $options[$option] = true;
                 }
             } else {
@@ -628,6 +595,9 @@ protected function readInput(): ?Document
         if (!$this->parser) {
             if ('-' !== $this->inputPath) {
                 $this->stdin = fopen($this->inputPath, 'r');
+                if (false === $this->stdin) {
+                    throw new InvalidDataException('Cannot open "'.$this->inputPath);
+                }
             }
 
             if ('mimedir' === $this->inputFormat) {
diff --git a/lib/Component.php b/lib/Component.php
index 2a08a082e..0849c5a8e 100644
--- a/lib/Component.php
+++ b/lib/Component.php
@@ -140,7 +140,7 @@ public function remove($item): void
             // If there's no dot in the name, it's an exact property name,
             // we can just wipe out all those properties.
             //
-            if (false === strpos($item, '.')) {
+            if (!str_contains($item, '.')) {
                 unset($this->children[strtoupper($item)]);
 
                 return;
@@ -210,8 +210,8 @@ public function select(string $name): array
     {
         $group = null;
         $name = strtoupper($name);
-        if (false !== strpos($name, '.')) {
-            list($group, $name) = explode('.', $name, 2);
+        if (str_contains($name, '.')) {
+            [$group, $name] = explode('.', $name, 2);
         }
         if ('' === $name) {
             $name = null;
@@ -228,9 +228,7 @@ public function select(string $name): array
             // more.
             return array_filter(
                 $result,
-                function ($child) use ($group) {
-                    return $child instanceof Property && (null !== $child->group ? strtoupper($child->group) : '') === $group;
-                }
+                fn ($child) => $child instanceof Property && (null !== $child->group ? strtoupper($child->group) : '') === $group
             );
         }
 
@@ -368,7 +366,7 @@ public function xmlSerialize(Xml\Writer $writer): void
 
         $writer->startElement(strtolower($this->name));
 
-        if (!empty($properties)) {
+        if ([] !== $properties) {
             $writer->startElement('properties');
 
             foreach ($properties as $property) {
@@ -378,7 +376,7 @@ public function xmlSerialize(Xml\Writer $writer): void
             $writer->endElement();
         }
 
-        if (!empty($components)) {
+        if ([] !== $components) {
             $writer->startElement('components');
 
             foreach ($components as $component) {
@@ -541,7 +539,7 @@ public function validate(int $options = 0): array
         $messages = [];
 
         foreach ($this->children() as $child) {
-            $name = strtoupper($child->name);
+            $name = strtoupper((string) $child->name);
             if (!isset($propertyCounters[$name])) {
                 $propertyCounters[$name] = 1;
             } else {
diff --git a/lib/Component/VAlarm.php b/lib/Component/VAlarm.php
index 0cb6ab1de..47474dfbf 100644
--- a/lib/Component/VAlarm.php
+++ b/lib/Component/VAlarm.php
@@ -32,9 +32,9 @@ class VAlarm extends VObject\Component
     public function getEffectiveTriggerTime(): \DateTimeImmutable
     {
         $trigger = $this->TRIGGER;
-        if (!isset($trigger['VALUE']) || ($trigger['VALUE'] && 'DURATION' === strtoupper($trigger['VALUE']))) {
+        if (!isset($trigger['VALUE']) || ($trigger['VALUE'] && 'DURATION' === strtoupper((string) $trigger['VALUE']))) {
             $triggerDuration = VObject\DateTimeParser::parseDuration($this->TRIGGER);
-            $related = (isset($trigger['RELATED']) && 'END' == strtoupper($trigger['RELATED'])) ? 'END' : 'START';
+            $related = (isset($trigger['RELATED']) && 'END' === strtoupper($trigger['RELATED'])) ? 'END' : 'START';
 
             /** @var VEvent|VTodo $parentComponent */
             $parentComponent = $this->parent;
diff --git a/lib/Component/VAvailability.php b/lib/Component/VAvailability.php
index ff6e9bd65..a4db47642 100644
--- a/lib/Component/VAvailability.php
+++ b/lib/Component/VAvailability.php
@@ -33,7 +33,7 @@ class VAvailability extends VObject\Component
      */
     public function isInTimeRange(\DateTimeInterface $start, \DateTimeInterface $end): bool
     {
-        list($effectiveStart, $effectiveEnd) = $this->getEffectiveStartEnd();
+        [$effectiveStart, $effectiveEnd] = $this->getEffectiveStartEnd();
 
         return
             (is_null($effectiveStart) || $start < $effectiveEnd)
diff --git a/lib/Component/VCalendar.php b/lib/Component/VCalendar.php
index 5163c042a..46928a62d 100644
--- a/lib/Component/VCalendar.php
+++ b/lib/Component/VCalendar.php
@@ -327,7 +327,7 @@ public function expand(\DateTimeInterface $start, \DateTimeInterface $end, ?\Dat
         foreach ($recurringEvents as $events) {
             try {
                 $it = new EventIterator($events, null, $timeZone);
-            } catch (NoInstancesException $e) {
+            } catch (NoInstancesException) {
                 // This event is recurring, but it doesn't have a single
                 // instance. We are skipping this event from the output
                 // entirely.
@@ -424,7 +424,7 @@ public function validate(int $options = 0): array
             if ($child instanceof Component) {
                 ++$componentsFound;
 
-                if (!in_array($child->name, ['VEVENT', 'VTODO', 'VJOURNAL'])) {
+                if (!in_array($child->name, ['VEVENT', 'VTODO', 'VJOURNAL'], true)) {
                     continue;
                 }
                 $componentTypes[] = $child->name;
diff --git a/lib/Component/VCard.php b/lib/Component/VCard.php
index 0dafb674b..7c5ca739c 100644
--- a/lib/Component/VCard.php
+++ b/lib/Component/VCard.php
@@ -423,10 +423,10 @@ public function getByType(string $propertyName, string $type)
      */
     public function getByTypes(string $propertyName, array $types)
     {
-        $types = array_map('strtolower', $types);
+        $types = array_map(strtolower(...), $types);
         foreach ($this->select($propertyName) as $field) {
             if (isset($field['TYPE'])) {
-                $parts = array_map('strtolower', $field['TYPE']->getParts());
+                $parts = array_map(strtolower(...), $field['TYPE']->getParts());
 
                 if (!array_diff($types, $parts) && !array_diff($parts, $types)) {
                     return $field;
@@ -491,9 +491,9 @@ public function xmlSerialize(Xml\Writer $writer): void
         $writer->startElement(strtolower($this->name));
 
         foreach ($propertiesByGroup as $group => $properties) {
-            if (!empty($group)) {
+            if ('' !== $group) {
                 $writer->startElement('group');
-                $writer->writeAttribute('name', strtolower($group));
+                $writer->writeAttribute('name', strtolower((string) $group));
             }
 
             foreach ($properties as $property) {
@@ -513,7 +513,7 @@ public function xmlSerialize(Xml\Writer $writer): void
                 }
             }
 
-            if (!empty($group)) {
+            if ('' !== $group) {
                 $writer->endElement();
             }
         }
@@ -529,7 +529,7 @@ public function getClassNameForPropertyName(string $propertyName): string
         $className = parent::getClassNameForPropertyName($propertyName);
 
         // In vCard 4, BINARY no longer exists, and we need URI instead.
-        if (VObject\Property\Binary::class == $className && self::VCARD40 === $this->getDocumentType()) {
+        if (VObject\Property\Binary::class === $className && self::VCARD40 === $this->getDocumentType()) {
             return VObject\Property\Uri::class;
         }
 
diff --git a/lib/Component/VEvent.php b/lib/Component/VEvent.php
index 6ca196d66..c13081884 100644
--- a/lib/Component/VEvent.php
+++ b/lib/Component/VEvent.php
@@ -44,7 +44,7 @@ public function isInTimeRange(\DateTimeInterface $start, \DateTimeInterface $end
         if ($this->RRULE || $this->RDATE) {
             try {
                 $it = new EventIterator($this, null, $start->getTimezone());
-            } catch (NoInstancesException $e) {
+            } catch (NoInstancesException) {
                 // If we've caught this exception, there are no instances
                 // for the event that fall into the specified time-range.
                 return false;
diff --git a/lib/Component/VFreeBusy.php b/lib/Component/VFreeBusy.php
index a9891c92c..623652ff9 100644
--- a/lib/Component/VFreeBusy.php
+++ b/lib/Component/VFreeBusy.php
@@ -41,7 +41,7 @@ public function isFree(\DateTimeInterface $start, \DatetimeInterface $end): bool
                 // Every period is formatted as [start]/[end]. The start is an
                 // absolute UTC time, the end may be an absolute UTC time, or
                 // duration (relative) value.
-                list($busyStart, $busyEnd) = explode('/', $period);
+                [$busyStart, $busyEnd] = explode('/', $period);
 
                 $busyStart = VObject\DateTimeParser::parse($busyStart);
                 $busyEnd = VObject\DateTimeParser::parse($busyEnd);
diff --git a/lib/DateTimeParser.php b/lib/DateTimeParser.php
index 712a40faf..9469cacea 100644
--- a/lib/DateTimeParser.php
+++ b/lib/DateTimeParser.php
@@ -42,7 +42,7 @@ public static function parseDateTime(string $dt, ?\DateTimeZone $tz = null): \Da
 
         try {
             $date = new \DateTimeImmutable($matches[1].'-'.$matches[2].'-'.$matches[3].' '.$matches[4].':'.$matches[5].':'.$matches[6], $tz);
-        } catch (\Exception $e) {
+        } catch (\Exception) {
             throw new InvalidDataException('The supplied iCalendar datetime value is incorrect: '.$dt);
         }
 
@@ -69,7 +69,7 @@ public static function parseDate(string $date, ?\DateTimeZone $tz = null): \Date
 
         try {
             $date = new \DateTimeImmutable($matches[1].'-'.$matches[2].'-'.$matches[3], $tz);
-        } catch (\Exception $e) {
+        } catch (\Exception) {
             throw new InvalidDataException('The supplied iCalendar date value is incorrect: '.$date);
         }
 
@@ -329,7 +329,7 @@ public static function parseVCardDateTime(string $date): array
 
         $result = [];
         foreach ($parts as $part) {
-            if (empty($matches[$part])) {
+            if (!array_key_exists($part, $matches) || '' === $matches[$part]) {
                 $result[$part] = null;
             } elseif ('-' === $matches[$part] || '--' === $matches[$part]) {
                 $result[$part] = null;
@@ -424,7 +424,7 @@ public static function parseVCardTime(string $date): array
 
         $result = [];
         foreach ($parts as $part) {
-            if (empty($matches[$part])) {
+            if (!array_key_exists($part, $matches) || '' === $matches[$part]) {
                 $result[$part] = null;
             } elseif ('-' === $matches[$part]) {
                 $result[$part] = null;
@@ -541,7 +541,7 @@ public static function parseVCardDateAndOrTime(string $date): array
         $parts['year0'] = &$parts['year'];
 
         foreach ($parts as $part => &$value) {
-            if (!empty($matches[$part])) {
+            if (array_key_exists($part, $matches) && '' !== $matches[$part]) {
                 $value = $matches[$part];
             }
         }
diff --git a/lib/Document.php b/lib/Document.php
index aa3a404a7..7cdb65d4f 100644
--- a/lib/Document.php
+++ b/lib/Document.php
@@ -118,10 +118,10 @@ public function getDocumentType(): int
     public function create(string $name)
     {
         if (isset(static::$componentMap[strtoupper($name)])) {
-            return call_user_func_array([$this, 'createComponent'], func_get_args());
+            return $this->createComponent(...func_get_args());
         }
 
-        return call_user_func_array([$this, 'createProperty'], func_get_args());
+        return $this->createProperty(...func_get_args());
     }
 
     /**
diff --git a/lib/FreeBusyData.php b/lib/FreeBusyData.php
index 405a5886d..6cdf2b937 100644
--- a/lib/FreeBusyData.php
+++ b/lib/FreeBusyData.php
@@ -11,25 +11,19 @@
  */
 class FreeBusyData
 {
-    /**
-     * Start timestamp.
-     */
-    protected int $start;
-
-    /**
-     * End timestamp.
-     */
-    protected int $end;
-
     /**
      * A list of free-busy times.
      */
     protected array $data;
 
-    public function __construct(int $start, int $end)
+    public function __construct(/**
+     * Start timestamp.
+     */
+        protected int $start, /**
+     * End timestamp.
+     */
+        protected int $end)
     {
-        $this->start = $start;
-        $this->end = $end;
         $this->data = [];
 
         $this->data[] = [
diff --git a/lib/FreeBusyGenerator.php b/lib/FreeBusyGenerator.php
index 424826034..3bcc842e3 100644
--- a/lib/FreeBusyGenerator.php
+++ b/lib/FreeBusyGenerator.php
@@ -217,7 +217,7 @@ function ($a, $b) {
         $new = [];
 
         foreach ($old as $vavail) {
-            list($compStart, $compEnd) = $vavail->getEffectiveStartEnd();
+            [$compStart, $compEnd] = $vavail->getEffectiveStartEnd();
 
             // We don't care about date-times that are earlier or later than the
             // start and end of the freebusy report, so this gets normalized
@@ -237,7 +237,7 @@ function ($a, $b) {
             // Going through our existing list of components to see if there's
             // a higher priority component that already fully covers this one.
             foreach ($new as $higherVavail) {
-                list($higherStart, $higherEnd) = $higherVavail->getEffectiveStartEnd();
+                [$higherStart, $higherEnd] = $higherVavail->getEffectiveStartEnd();
                 if (
                     (is_null($higherStart) || $higherStart < $compStart)
                     && (is_null($higherEnd) || $higherEnd > $compEnd)
@@ -259,7 +259,7 @@ function ($a, $b) {
         // priority components to override the lower ones.
         foreach (array_reverse($new) as $vavail) {
             $busyType = isset($vavail->BUSYTYPE) ? strtoupper($vavail->BUSYTYPE) : 'BUSY-UNAVAILABLE';
-            list($vavailStart, $vavailEnd) = $vavail->getEffectiveStartEnd();
+            [$vavailStart, $vavailEnd] = $vavail->getEffectiveStartEnd();
 
             // Making the component size no larger than the requested free-busy
             // report range.
@@ -281,7 +281,7 @@ function ($a, $b) {
             // Looping over the AVAILABLE components.
             if (isset($vavail->AVAILABLE)) {
                 foreach ($vavail->AVAILABLE as $available) {
-                    list($availStart, $availEnd) = $available->getEffectiveStartEnd();
+                    [$availStart, $availEnd] = $available->getEffectiveStartEnd();
                     $fbData->add(
                         $availStart->getTimeStamp(),
                         $availEnd->getTimeStamp(),
@@ -362,7 +362,7 @@ protected function calculateBusy(FreeBusyData $fbData, array $objects): void
                         if ($component->RRULE) {
                             try {
                                 $iterator = new EventIterator($object, (string) $component->UID, $this->timeZone);
-                            } catch (NoInstancesException $e) {
+                            } catch (NoInstancesException) {
                                 // This event is recurring, but it doesn't have a single
                                 // instance. We are skipping this event from the output
                                 // entirely.
@@ -437,12 +437,12 @@ protected function calculateBusy(FreeBusyData $fbData, array $objects): void
                                 continue;
                             }
 
-                            $values = explode(',', $freebusy);
+                            $values = explode(',', (string) $freebusy);
                             foreach ($values as $value) {
-                                list($startTime, $endTime) = explode('/', $value);
+                                [$startTime, $endTime] = explode('/', $value);
                                 $startTime = DateTimeParser::parseDateTime($startTime);
 
-                                if ('P' === substr($endTime, 0, 1) || '-P' === substr($endTime, 0, 2)) {
+                                if (str_starts_with($endTime, 'P') || str_starts_with($endTime, '-P')) {
                                     $duration = DateTimeParser::parseDuration($endTime);
                                     $endTime = clone $startTime;
                                     $endTime = $endTime->add($duration);
@@ -507,7 +507,7 @@ protected function generateFreeBusyCalendar(FreeBusyData $fbData): VCalendar
         $vfreebusy->add($dtstamp);
 
         foreach ($fbData->getData() as $busyTime) {
-            $busyType = strtoupper($busyTime['type']);
+            $busyType = strtoupper((string) $busyTime['type']);
 
             // Ignoring all the FREE parts, because those are already assumed.
             if ('FREE' === $busyType) {
diff --git a/lib/ITip/Broker.php b/lib/ITip/Broker.php
index 9bcdcc2a2..42862cd8b 100644
--- a/lib/ITip/Broker.php
+++ b/lib/ITip/Broker.php
@@ -228,7 +228,7 @@ public function parseEvent($calendar, $userHref, $oldCalendar = null): array
 
             $eventInfo = $oldEventInfo;
 
-            if (in_array($eventInfo['organizer'], $userHref)) {
+            if (in_array($eventInfo['organizer'], $userHref, true)) {
                 // This is an organizer deleting the event.
                 $eventInfo['attendees'] = [];
                 // Increasing the sequence, but only if the organizer deleted
@@ -237,7 +237,7 @@ public function parseEvent($calendar, $userHref, $oldCalendar = null): array
             } else {
                 // This is an attendee deleting the event.
                 foreach ($eventInfo['attendees'] as $key => $attendee) {
-                    if (in_array($attendee['href'], $userHref)) {
+                    if (in_array($attendee['href'], $userHref, true)) {
                         $eventInfo['attendees'][$key]['instances'] = ['master' => ['id' => 'master', 'partstat' => 'DECLINED'],
                         ];
                     }
@@ -247,13 +247,13 @@ public function parseEvent($calendar, $userHref, $oldCalendar = null): array
         }
 
         // Check if the user is the organizer
-        if (in_array($eventInfo['organizer'], $userHref)) {
+        if (in_array($eventInfo['organizer'], $userHref, true)) {
             return $this->parseEventForOrganizer($baseCalendar, $eventInfo, $oldEventInfo);
         }
 
         // Check if the user is an attendee
         foreach ($eventInfo['attendees'] as $attendee) {
-            if (in_array($attendee['href'], $userHref)) {
+            if (in_array($attendee['href'], $userHref, true)) {
                 // If this is a event update, we always generate a reply
                 if ($oldCalendar) {
                     return $this->parseEventForAttendee($baseCalendar, $eventInfo, $oldEventInfo, $attendee['href']);
@@ -354,7 +354,7 @@ protected function processMessageReply(Message $itipMessage, ?VCalendar $existin
             $instances[$recurId] = $attendee['PARTSTAT']->getValue();
             if (isset($vevent->{'REQUEST-STATUS'})) {
                 $requestStatus = $vevent->{'REQUEST-STATUS'}->getValue();
-                list($requestStatus) = explode(';', $requestStatus);
+                [$requestStatus] = explode(';', $requestStatus);
             }
         }
 
@@ -566,7 +566,7 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
 
                 $message->significantChange =
                     'REQUEST' === $attendee['forceSend']
-                    || count($oldAttendeeInstances) != count($newAttendeeInstances)
+                    || count($oldAttendeeInstances) !== count($newAttendeeInstances)
                     || count(array_diff($oldAttendeeInstances, $newAttendeeInstances)) > 0
                     || $oldEventInfo['significantChangeHash'] !== $eventInfo['significantChangeHash'];
 
@@ -576,9 +576,9 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
                         // We need to find a list of events that the attendee
                         // is not a part of to add to the list of exceptions.
                         $exceptions = [];
-                        foreach ($eventInfo['instances'] as $instanceId => $vevent) {
-                            if (!isset($attendee['newInstances'][$instanceId])) {
-                                $exceptions[] = $instanceId;
+                        foreach ($eventInfo['instances'] as $eventInstanceId => $vevent) {
+                            if (!isset($attendee['newInstances'][$eventInstanceId])) {
+                                $exceptions[] = $eventInstanceId;
                             }
                         }
 
@@ -648,7 +648,12 @@ protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo,
             return [];
         }
 
-        $oldInstances = !empty($oldEventInfo['attendees'][$attendee]['instances']) ?
+        $oldInstances =
+            is_array($oldEventInfo['attendees'])
+            && array_key_exists($attendee, $oldEventInfo['attendees'])
+            && is_array($oldEventInfo['attendees'][$attendee])
+            && array_key_exists('instances', $oldEventInfo['attendees'][$attendee])
+            && is_array($oldEventInfo['attendees'][$attendee]['instances']) ?
             $oldEventInfo['attendees'][$attendee]['instances'] :
             [];
 
@@ -679,7 +684,7 @@ protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo,
         // We only need to do that though, if the master event is not declined.
         if (isset($instances['master']) && 'DECLINED' !== $instances['master']['newstatus']) {
             foreach ($eventInfo['exdate'] as $exDate) {
-                if (!in_array($exDate, $oldEventInfo['exdate'] ?? [])) {
+                if (!in_array($exDate, $oldEventInfo['exdate'] ?? [], true)) {
                     if (isset($instances[$exDate])) {
                         $instances[$exDate]['newstatus'] = 'DECLINED';
                     } else {
@@ -722,7 +727,7 @@ protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo,
         $hasReply = false;
 
         foreach ($instances as $instance) {
-            if ($instance['oldstatus'] == $instance['newstatus'] && 'REPLY' !== $eventInfo['organizerForceSend']) {
+            if ($instance['oldstatus'] === $instance['newstatus'] && 'REPLY' !== $eventInfo['organizerForceSend']) {
                 // Skip
                 continue;
             }
@@ -754,7 +759,7 @@ protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo,
                 // EXDATE
                 $dt = DateTimeParser::parse($instance['id'], $eventInfo['timezone']);
                 // Treat is as a DATE field
-                if (strlen($instance['id']) <= 8) {
+                if (strlen((string) $instance['id']) <= 8) {
                     $event->add('DTSTART', $dt, ['VALUE' => 'DATE']);
                 } else {
                     $event->add('DTSTART', $dt);
@@ -766,7 +771,7 @@ protected function parseEventForAttendee(VCalendar $calendar, array $eventInfo,
             if ('master' !== $instance['id']) {
                 $dt = DateTimeParser::parse($instance['id'], $eventInfo['timezone']);
                 // Treat is as a DATE field
-                if (strlen($instance['id']) <= 8) {
+                if (strlen((string) $instance['id']) <= 8) {
                     $event->add('RECURRENCE-ID', $dt, ['VALUE' => 'DATE']);
                 } else {
                     $event->add('RECURRENCE-ID', $dt);
@@ -858,7 +863,7 @@ protected function parseEventInfo(VCalendar $calendar): array
                     $organizer = $vevent->ORGANIZER->getNormalizedValue();
                     $organizerName = $vevent->ORGANIZER['CN'] ?? null;
                 } else {
-                    if (strtoupper($organizer) !== strtoupper($vevent->ORGANIZER->getNormalizedValue())) {
+                    if (strtoupper($organizer) !== strtoupper((string) $vevent->ORGANIZER->getNormalizedValue())) {
                         throw new SameOrganizerForAllComponentsException('Every instance of the event must have the same organizer.');
                     }
                 }
@@ -884,7 +889,7 @@ protected function parseEventInfo(VCalendar $calendar): array
                 foreach ($vevent->select('RRULE') as $rr) {
                     foreach ($rr->getParts() as $key => $val) {
                         // ignore default values (https://github.com/sabre-io/vobject/issues/126)
-                        if ('INTERVAL' === $key && 1 == $val) {
+                        if ('INTERVAL' === $key && '1' === (string) $val) {
                             continue;
                         }
                         if (is_array($val)) {
@@ -896,7 +901,7 @@ protected function parseEventInfo(VCalendar $calendar): array
                 sort($rrule);
             }
             if (isset($vevent->STATUS)) {
-                $status = strtoupper($vevent->STATUS->getValue());
+                $status = strtoupper((string) $vevent->STATUS->getValue());
             }
 
             $recurId = isset($vevent->{'RECURRENCE-ID'}) ? $vevent->{'RECURRENCE-ID'}->getValue() : 'master';
@@ -914,7 +919,7 @@ protected function parseEventInfo(VCalendar $calendar): array
                 foreach ($vevent->ATTENDEE as $attendee) {
                     if ($this->scheduleAgentServerRules
                         && isset($attendee['SCHEDULE-AGENT'])
-                        && 'CLIENT' === strtoupper($attendee['SCHEDULE-AGENT']->getValue())
+                        && 'CLIENT' === strtoupper((string) $attendee['SCHEDULE-AGENT']->getValue())
                     ) {
                         continue;
                     }
@@ -951,6 +956,7 @@ protected function parseEventInfo(VCalendar $calendar): array
             }
 
             foreach ($this->significantChangeProperties as $prop) {
+                // @phpstan-ignore property.dynamicName
                 if (isset($vevent->$prop)) {
                     $propertyValues = $vevent->select($prop);
 
diff --git a/lib/ITip/Message.php b/lib/ITip/Message.php
index 6f59eebc2..505e07f25 100644
--- a/lib/ITip/Message.php
+++ b/lib/ITip/Message.php
@@ -32,12 +32,12 @@ class Message
      * Contains the ITip method, which is something like REQUEST, REPLY or
      * CANCEL.
      */
-    public ?string $method;
+    public ?string $method = null;
 
     /**
      * The current sequence number for the event.
      */
-    public ?int $sequence;
+    public ?int $sequence = null;
 
     /**
      * The senders' email address.
@@ -52,7 +52,7 @@ class Message
      * The name of the sender. This is often populated from a CN parameter from
      * either the ORGANIZER or ATTENDEE, depending on the message.
      */
-    public ?string $senderName;
+    public ?string $senderName = null;
 
     /**
      * The recipient's email address.
@@ -63,7 +63,7 @@ class Message
      * The name of the recipient. This is usually populated with the CN
      * parameter from the ATTENDEE or ORGANIZER property, if it's available.
      */
-    public ?string $recipientName;
+    public ?string $recipientName = null;
 
     /**
      * After the message has been delivered, this should contain a string such
@@ -108,7 +108,7 @@ public function getScheduleStatus()
         if (!$this->scheduleStatus) {
             return false;
         }
-        list($scheduleStatus) = explode(';', $this->scheduleStatus);
+        [$scheduleStatus] = explode(';', $this->scheduleStatus);
 
         return $scheduleStatus;
     }
diff --git a/lib/Node.php b/lib/Node.php
index 0dbe7cfad..47889a2ab 100644
--- a/lib/Node.php
+++ b/lib/Node.php
@@ -42,7 +42,7 @@ abstract class Node implements \IteratorAggregate, \ArrayAccess, \Countable, \Js
     /**
      * Reference to the parent object, if this is not the top object.
      */
-    public ?Node $parent;
+    public ?Node $parent = null;
 
     /**
      * Iterator override.
@@ -52,7 +52,7 @@ abstract class Node implements \IteratorAggregate, \ArrayAccess, \Countable, \Js
     /**
      * The root document.
      */
-    protected ?Component $root;
+    protected ?Component $root = null;
 
     /**
      * Serializes the node into a mimedir format.
diff --git a/lib/PHPUnitAssertions.php b/lib/PHPUnitAssertions.php
index 1976c3afd..aad5438a5 100644
--- a/lib/PHPUnitAssertions.php
+++ b/lib/PHPUnitAssertions.php
@@ -41,7 +41,7 @@ public function assertVObjectEqualsVObject($expected, $actual, string $message =
                 $input = Reader::read($input);
             }
             if (!$input instanceof Component) {
-                $this->fail('Input must be a string, stream or VObject component');
+                self::fail('Input must be a string, stream or VObject component');
             }
             unset($input->PRODID);
             if ($input instanceof Component\VCalendar && 'GREGORIAN' === (string) $input->CALSCALE) {
@@ -51,23 +51,28 @@ public function assertVObjectEqualsVObject($expected, $actual, string $message =
             return $input;
         };
 
-        $expected = $getObj($expected)->serialize();
-        $actual = $getObj($actual)->serialize();
+        /**
+         * @var string $expectedSerialized
+         */
+        $expectedSerialized = $getObj($expected)->serialize();
+        $actualSerialized = $getObj($actual)->serialize();
 
         // Finding wildcards in expected.
-        preg_match_all('|^([A-Z]+):\\*\\*ANY\\*\\*\r$|m', $expected, $matches, PREG_SET_ORDER);
+        $result = preg_match_all('|^([A-Z]+):\\*\\*ANY\\*\\*\r$|m', $expectedSerialized, $matches, PREG_SET_ORDER);
+
+        self::assertNotFalse($result);
 
         foreach ($matches as $match) {
-            $actual = preg_replace(
+            $actualSerialized = preg_replace(
                 '|^'.preg_quote($match[1], '|').':(.*)\r$|m',
                 $match[1].':**ANY**'."\r",
-                $actual
+                (string) $actualSerialized
             );
         }
 
-        $this->assertEquals(
-            $expected,
-            $actual,
+        self::assertEquals(
+            $expectedSerialized,
+            $actualSerialized,
             $message
         );
     }
diff --git a/lib/Parameter.php b/lib/Parameter.php
index 9952d3d2b..64f77c187 100644
--- a/lib/Parameter.php
+++ b/lib/Parameter.php
@@ -16,7 +16,7 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
  */
-class Parameter extends Node
+class Parameter extends Node implements \Stringable
 {
     /**
      * Parameter name.
@@ -74,83 +74,12 @@ public function __construct(Document $root, ?string $name, $value = null)
      */
     public static function guessParameterNameByValue(string $value): string
     {
-        switch (strtoupper($value)) {
-            // Encodings
-            case '7-BIT':
-            case 'QUOTED-PRINTABLE':
-            case 'BASE64':
-                $name = 'ENCODING';
-                break;
-
-                // Common types
-            case 'WORK':
-            case 'HOME':
-            case 'PREF':
-                // Delivery Label Type
-            case 'DOM':
-            case 'INTL':
-            case 'POSTAL':
-            case 'PARCEL':
-                // Telephone types
-            case 'VOICE':
-            case 'FAX':
-            case 'MSG':
-            case 'CELL':
-            case 'PAGER':
-            case 'BBS':
-            case 'MODEM':
-            case 'CAR':
-            case 'ISDN':
-            case 'VIDEO':
-                // EMAIL types (lol)
-            case 'AOL':
-            case 'APPLELINK':
-            case 'ATTMAIL':
-            case 'CIS':
-            case 'EWORLD':
-            case 'INTERNET':
-            case 'IBMMAIL':
-            case 'MCIMAIL':
-            case 'POWERSHARE':
-            case 'PRODIGY':
-            case 'TLX':
-            case 'X400':
-                // Photo / Logo format types
-            case 'GIF':
-            case 'CGM':
-            case 'WMF':
-            case 'BMP':
-            case 'DIB':
-            case 'PICT':
-            case 'TIFF':
-            case 'PDF':
-            case 'PS':
-            case 'JPEG':
-            case 'MPEG':
-            case 'MPEG2':
-            case 'AVI':
-            case 'QTIME':
-                // Sound Digital Audio Type
-            case 'WAVE':
-            case 'PCM':
-            case 'AIFF':
-                // Key types
-            case 'X509':
-            case 'PGP':
-                $name = 'TYPE';
-                break;
-
-                // Value types
-            case 'INLINE':
-            case 'URL':
-            case 'CONTENT-ID':
-            case 'CID':
-                $name = 'VALUE';
-                break;
-
-            default:
-                $name = '';
-        }
+        $name = match (strtoupper($value)) {
+            '7-BIT', 'QUOTED-PRINTABLE', 'BASE64' => 'ENCODING',
+            'WORK', 'HOME', 'PREF', 'DOM', 'INTL', 'POSTAL', 'PARCEL', 'VOICE', 'FAX', 'MSG', 'CELL', 'PAGER', 'BBS', 'MODEM', 'CAR', 'ISDN', 'VIDEO', 'AOL', 'APPLELINK', 'ATTMAIL', 'CIS', 'EWORLD', 'INTERNET', 'IBMMAIL', 'MCIMAIL', 'POWERSHARE', 'PRODIGY', 'TLX', 'X400', 'GIF', 'CGM', 'WMF', 'BMP', 'DIB', 'PICT', 'TIFF', 'PDF', 'PS', 'JPEG', 'MPEG', 'MPEG2', 'AVI', 'QTIME', 'WAVE', 'PCM', 'AIFF', 'X509', 'PGP' => 'TYPE',
+            'INLINE', 'URL', 'CONTENT-ID', 'CID' => 'VALUE',
+            default => '',
+        };
 
         return $name;
     }
@@ -234,7 +163,8 @@ public function has(string $value): bool
     {
         return in_array(
             strtolower($value),
-            array_map('strtolower', (array) $this->value)
+            array_map(strtolower(...), (array) $this->value),
+            true
         );
     }
 
diff --git a/lib/Parser/Json.php b/lib/Parser/Json.php
index 6403af4e9..45f985f68 100644
--- a/lib/Parser/Json.php
+++ b/lib/Parser/Json.php
@@ -27,12 +27,12 @@ class Json extends Parser
     /**
      * The input data.
      */
-    protected ?array $input;
+    protected ?array $input = null;
 
     /**
      * Root component.
      */
-    protected ?Document $root;
+    protected ?Document $root = null;
 
     /**
      * This method starts the parsing process.
@@ -61,16 +61,11 @@ public function parse($input = null, int $options = 0): ?Document
             $this->options = $options;
         }
 
-        switch ($this->input[0]) {
-            case 'vcalendar':
-                $this->root = new VCalendar([], false);
-                break;
-            case 'vcard':
-                $this->root = new VCard([], false);
-                break;
-            default:
-                throw new ParseException('The root component must either be a vcalendar, or a vcard');
-        }
+        $this->root = match ($this->input[0]) {
+            'vcalendar' => new VCalendar([], false),
+            'vcard' => new VCard([], false),
+            default => throw new ParseException('The root component must either be a vcalendar, or a vcard'),
+        };
         foreach ($this->input[1] as $prop) {
             $this->root->add($this->parseProperty($prop));
         }
@@ -97,17 +92,13 @@ public function parseComponent(array $jComp): Component
         $self = $this;
 
         $properties = array_map(
-            function ($jProp) use ($self) {
-                return $self->parseProperty($jProp);
-            },
+            $self->parseProperty(...),
             $jComp[1]
         );
 
         if (isset($jComp[2])) {
             $components = array_map(
-                function ($jComp) use ($self) {
-                    return $self->parseComponent($jComp);
-                },
+                $self->parseComponent(...),
                 $jComp[2]
             );
         } else {
@@ -134,7 +125,7 @@ public function parseProperty(array $jProp): Property
             $valueType,
         ) = $jProp;
 
-        $propertyName = strtoupper($propertyName);
+        $propertyName = strtoupper((string) $propertyName);
 
         // This is the default class we would be using if we didn't know the
         // value type. We're using this value later in this function.
@@ -144,7 +135,7 @@ public function parseProperty(array $jProp): Property
 
         $value = array_slice($jProp, 3);
 
-        $valueType = strtoupper($valueType);
+        $valueType = strtoupper((string) $valueType);
 
         if (isset($parameters['group'])) {
             $propertyName = $parameters['group'].'.'.$propertyName;
@@ -165,7 +156,7 @@ public function parseProperty(array $jProp): Property
         // If the value type we received (e.g.: TEXT) was not the default value
         // type for the given property (e.g.: BDAY), we need to add a VALUE=
         // parameter.
-        if ($defaultPropertyClass !== get_class($prop)) {
+        if ($defaultPropertyClass !== $prop::class) {
             $prop['VALUE'] = $valueType;
         }
 
diff --git a/lib/Parser/MimeDir.php b/lib/Parser/MimeDir.php
index 7718dba04..47fa972ce 100644
--- a/lib/Parser/MimeDir.php
+++ b/lib/Parser/MimeDir.php
@@ -41,7 +41,7 @@ class MimeDir extends Parser
     /**
      * Root component.
      */
-    protected ?Document $root;
+    protected ?Document $root = null;
 
     /**
      * By default, all input will be assumed to be UTF-8.
@@ -111,7 +111,7 @@ public function parse($input = null, int $options = 0): ?Document
      */
     public function setCharset(string $charset): void
     {
-        if (!in_array($charset, self::$SUPPORTED_CHARSETS)) {
+        if (!in_array($charset, self::$SUPPORTED_CHARSETS, true)) {
             throw new \InvalidArgumentException('Unsupported encoding. (Supported encodings: '.implode(', ', self::$SUPPORTED_CHARSETS).')');
         }
         $this->charset = $charset;
@@ -155,23 +155,18 @@ protected function parseDocument(): void
 
         // BOM is ZERO WIDTH NO-BREAK SPACE (U+FEFF).
         // It's 0xEF 0xBB 0xBF in UTF-8 hex.
-        if (3 <= strlen($line)
+        if (3 <= strlen((string) $line)
             && 0xEF === ord($line[0])
             && 0xBB === ord($line[1])
             && 0xBF === ord($line[2])) {
-            $line = \substr($line, 3);
+            $line = \substr((string) $line, 3);
         }
 
-        switch (strtoupper($line)) {
-            case 'BEGIN:VCALENDAR':
-                $class = VCalendar::$componentMap['VCALENDAR'];
-                break;
-            case 'BEGIN:VCARD':
-                $class = VCard::$componentMap['VCARD'];
-                break;
-            default:
-                throw new ParseException('This parser only supports VCARD and VCALENDAR files');
-        }
+        $class = match (strtoupper((string) $line)) {
+            'BEGIN:VCALENDAR' => VCalendar::$componentMap['VCALENDAR'],
+            'BEGIN:VCARD' => VCard::$componentMap['VCARD'],
+            default => throw new ParseException('This parser only supports VCARD and VCALENDAR files'),
+        };
 
         $this->root = new $class([], false);
 
@@ -179,10 +174,10 @@ protected function parseDocument(): void
             // Reading until we hit END:
             try {
                 $line = $this->readLine();
-            } catch (EofException $oEx) {
+            } catch (EofException) {
                 $line = 'END:'.$this->root->name;
             }
-            if ('END:' === strtoupper(\substr($line, 0, 4))) {
+            if ('END:' === strtoupper(\substr((string) $line, 0, 4))) {
                 break;
             }
             $result = $this->parseLine($line);
@@ -191,7 +186,7 @@ protected function parseDocument(): void
             }
         }
 
-        $name = strtoupper(\substr($line, 4));
+        $name = strtoupper(\substr((string) $line, 4));
         if ($name !== $this->root->name) {
             throw new ParseException('Invalid MimeDir file. expected: "END:'.$this->root->name.'" got: "END:'.$name.'"');
         }
@@ -220,7 +215,7 @@ protected function parseLine(string $line)
             while (true) {
                 // Reading until we hit END:
                 $line = $this->readLine();
-                if ('END:' === strtoupper(\substr($line, 0, 4))) {
+                if ('END:' === strtoupper(\substr((string) $line, 0, 4))) {
                     break;
                 }
                 $result = $this->parseLine($line);
@@ -229,7 +224,7 @@ protected function parseLine(string $line)
                 }
             }
 
-            $name = strtoupper(\substr($line, 4));
+            $name = strtoupper(\substr((string) $line, 4));
             if ($name !== $component->name) {
                 throw new ParseException('Invalid MimeDir file. expected: "END:'.$component->name.'" got: "END:'.$name.'"');
             }
@@ -401,7 +396,7 @@ protected function readProperty(string $line)
                     throw new ParseException('Invalid Mimedir file. Line starting at '.$this->startLine.' did not follow iCalendar/vCard conventions');
                 }
 
-                if ('=' == $match[0][0] && self::TOKEN_PARAMNAME != $lastToken) {
+                if ('=' === $match[0][0] && self::TOKEN_PARAMNAME !== $lastToken) {
                     throw new ParseException('Invalid Mimedir file. Line starting at '.$this->startLine.': Missing parameter name for parameter value "'.$match['paramValue'].'"');
                 }
 
@@ -448,7 +443,7 @@ protected function readProperty(string $line)
         if (\is_null($property['value'])) {
             $property['value'] = '';
         }
-        if (!isset($property['name']) || 0 == strlen($property['name'])) {
+        if (!isset($property['name']) || 0 === strlen($property['name'])) {
             if ($this->options & self::OPTION_IGNORE_INVALID_LINES) {
                 return false;
             }
@@ -691,7 +686,7 @@ private function extractQuotedPrintableValue(): string
         // missing a whitespace. So if 'forgiving' is turned on, we will take
         // those as well.
         if ($this->options & self::OPTION_FORGIVING) {
-            while ('=' === \substr($value, -1) && $this->lineBuffer) {
+            while (str_ends_with($value, '=') && $this->lineBuffer) {
                 // Reading the line
                 $this->readLine();
                 // Grabbing the raw form
diff --git a/lib/Parser/Parser.php b/lib/Parser/Parser.php
index 29921d182..c5126445a 100644
--- a/lib/Parser/Parser.php
+++ b/lib/Parser/Parser.php
@@ -30,11 +30,6 @@ abstract class Parser
      */
     public const OPTION_IGNORE_INVALID_LINES = 2;
 
-    /**
-     * Bitmask of parser options.
-     */
-    protected int $options;
-
     /**
      * Creates the parser.
      *
@@ -42,12 +37,11 @@ abstract class Parser
      *
      * @param int $options any parser options (OPTION constants)
      */
-    public function __construct($input = null, int $options = 0)
+    public function __construct($input = null, protected int $options = 0)
     {
         if (!is_null($input)) {
             $this->setInput($input);
         }
-        $this->options = $options;
     }
 
     /**
diff --git a/lib/Parser/XML.php b/lib/Parser/XML.php
index 9a5100684..6fb3e5624 100644
--- a/lib/Parser/XML.php
+++ b/lib/Parser/XML.php
@@ -28,17 +28,17 @@ class XML extends Parser
     /**
      * The input data.
      */
-    protected ?array $input;
+    protected ?array $input = null;
 
     /**
      * A pointer/reference to the input.
      */
-    private ?array $pointer;
+    private ?array $pointer = null;
 
     /**
      * Document, root component.
      */
-    protected ?Document $root;
+    protected ?Document $root = null;
 
     /**
      * Creates the parser.
@@ -112,7 +112,7 @@ public function parse($input = null, int $options = 0): ?Document
      */
     protected function parseVCalendarComponents(Component $parentComponent): void
     {
-        foreach ($this->pointer['value'] ?: [] as $children) {
+        foreach ($this->pointer['value'] ?? [] as $children) {
             switch (static::getTagName($children['name'])) {
                 case 'properties':
                     $this->pointer = &$children['value'];
@@ -145,8 +145,8 @@ protected function parseVCardComponents(Component $parentComponent): void
      */
     protected function parseProperties(Component $parentComponent, string $propertyNamePrefix = ''): void
     {
-        foreach ($this->pointer ?: [] as $xmlProperty) {
-            list($namespace, $tagName) = SabreXml\Service::parseClarkNotation($xmlProperty['name']);
+        foreach ($this->pointer ?? [] as $xmlProperty) {
+            [$namespace, $tagName] = SabreXml\Service::parseClarkNotation($xmlProperty['name']);
 
             $propertyName = $tagName;
             $propertyValue = [];
@@ -301,7 +301,7 @@ protected function parseProperties(Component $parentComponent, string $propertyN
      */
     protected function parseComponent(Component $parentComponent): void
     {
-        $components = $this->pointer['value'] ?: [];
+        $components = $this->pointer['value'] ?? [];
 
         foreach ($components as $component) {
             $componentName = static::getTagName($component['name']);
diff --git a/lib/Property.php b/lib/Property.php
index 56b571e51..7432e5064 100644
--- a/lib/Property.php
+++ b/lib/Property.php
@@ -14,27 +14,8 @@
  * @author Evert Pot (http://evertpot.com/)
  * @license http://sabre.io/license/ Modified BSD License
  */
-abstract class Property extends Node
+abstract class Property extends Node implements \Stringable
 {
-    /**
-     * The root document.
-     */
-    public ?Component $root;
-
-    /**
-     * Property name.
-     *
-     * This will contain a string such as DTSTART, SUMMARY, FN.
-     */
-    public ?string $name;
-
-    /**
-     * Property group.
-     *
-     * This is only used in vcards
-     */
-    public ?string $group;
-
     /**
      * List of parameters.
      */
@@ -75,13 +56,13 @@ abstract class Property extends Node
      * @param array             $parameters List of parameters
      * @param string|null       $group      The vcard property group
      */
-    public function __construct(Component $root, ?string $name, $value = null, array $parameters = [], ?string $group = null, ?int $lineIndex = null, ?string $lineString = null)
+    public function __construct(public ?Component $root, /**
+     * Property name.
+     *
+     * This will contain a string such as DTSTART, SUMMARY, FN.
+     */
+        public ?string $name, $value = null, array $parameters = [], public ?string $group = null, ?int $lineIndex = null, ?string $lineString = null)
     {
-        $this->name = $name;
-        $this->group = $group;
-
-        $this->root = $root;
-
         foreach ($parameters as $k => $v) {
             $this->add($k, $v);
         }
@@ -123,7 +104,7 @@ public function setValue($value): void
     public function getValue()
     {
         if (is_array($this->value)) {
-            if (0 == count($this->value)) {
+            if (0 === count($this->value)) {
                 return null;
             } elseif (1 === count($this->value)) {
                 return $this->value[0];
@@ -242,7 +223,7 @@ public function serialize(): string
         );
 
         // remove single space after last CRLF
-        return \substr($str, 0, -1);
+        return \substr((string) $str, 0, -1);
     }
 
     /**
@@ -282,7 +263,7 @@ public function jsonSerialize(): array
             if ('VALUE' === $parameter->name) {
                 continue;
             }
-            $parameters[strtolower($parameter->name)] = $parameter->jsonSerialize();
+            $parameters[strtolower((string) $parameter->name)] = $parameter->jsonSerialize();
         }
         // In jCard, we need to encode the property-group as a separate 'group'
         // parameter.
@@ -292,7 +273,7 @@ public function jsonSerialize(): array
 
         return array_merge(
             [
-                strtolower($this->name),
+                strtolower((string) $this->name),
                 (object) $parameters,
                 strtolower($this->getValueType()),
             ],
@@ -329,13 +310,13 @@ public function xmlSerialize(Xml\Writer $writer): void
             $parameters[] = $parameter;
         }
 
-        $writer->startElement(strtolower($this->name));
+        $writer->startElement(strtolower((string) $this->name));
 
-        if (!empty($parameters)) {
+        if ([] !== $parameters) {
             $writer->startElement('parameters');
 
             foreach ($parameters as $parameter) {
-                $writer->startElement(strtolower($parameter->name));
+                $writer->startElement(strtolower((string) $parameter->name));
                 $writer->write($parameter);
                 $writer->endElement();
             }
@@ -520,7 +501,7 @@ public function validate(int $options = 0): array
         }
 
         // Checking if the property name does not contain any invalid bytes.
-        if (!preg_match('/^([A-Z0-9-]+)$/', $this->name)) {
+        if (!preg_match('/^([A-Z0-9-]+)$/', (string) $this->name)) {
             $warnings[] = [
                 'level' => $options & self::REPAIR ? 1 : 3,
                 'message' => 'The property name: '.$this->name.' contains invalid characters. Only A-Z, 0-9 and - are allowed',
@@ -572,7 +553,7 @@ public function validate(int $options = 0): array
                         }
                         break;
                 }
-                if ($allowedEncoding && !in_array(strtoupper($encoding), $allowedEncoding)) {
+                if ($allowedEncoding && !in_array(strtoupper($encoding), $allowedEncoding, true)) {
                     $warnings[] = [
                         'level' => 3,
                         'message' => 'ENCODING='.strtoupper($encoding).' is not valid for this document type.',
diff --git a/lib/Property/Binary.php b/lib/Property/Binary.php
index 25cda8d25..9d68f415e 100644
--- a/lib/Property/Binary.php
+++ b/lib/Property/Binary.php
@@ -54,7 +54,7 @@ public function setValue($value): void
      */
     public function setRawMimeDirValue(string $val): void
     {
-        $this->value = base64_decode($val);
+        $this->value = base64_decode($val, true);
     }
 
     /**
@@ -62,7 +62,7 @@ public function setRawMimeDirValue(string $val): void
      */
     public function getRawMimeDirValue(): string
     {
-        return base64_encode($this->value);
+        return base64_encode((string) $this->value);
     }
 
     /**
@@ -83,7 +83,7 @@ public function getValueType(): string
      */
     public function getJsonValue(): array
     {
-        return [base64_encode($this->getValue())];
+        return [base64_encode((string) $this->getValue())];
     }
 
     /**
@@ -93,7 +93,7 @@ public function getJsonValue(): array
      */
     public function setJsonValue(array $value): void
     {
-        $value = array_map('base64_decode', $value);
+        $value = array_map(base64_decode(...), $value);
         parent::setJsonValue($value);
     }
 }
diff --git a/lib/Property/Boolean.php b/lib/Property/Boolean.php
index cdc3408aa..f33fbafdc 100644
--- a/lib/Property/Boolean.php
+++ b/lib/Property/Boolean.php
@@ -56,9 +56,7 @@ public function getValueType(): string
     public function setXmlValue(array $value): void
     {
         $value = array_map(
-            function ($value) {
-                return 'true' === $value;
-            },
+            fn ($value) => 'true' === $value,
             $value
         );
         parent::setXmlValue($value);
diff --git a/lib/Property/FloatValue.php b/lib/Property/FloatValue.php
index 7a36e0976..32b02a972 100644
--- a/lib/Property/FloatValue.php
+++ b/lib/Property/FloatValue.php
@@ -67,7 +67,7 @@ public function getValueType(): string
      */
     public function getJsonValue(): array
     {
-        $val = array_map('floatval', $this->getParts());
+        $val = array_map(floatval(...), $this->getParts());
 
         // Special-casing the GEO property.
         //
@@ -86,7 +86,7 @@ public function getJsonValue(): array
      */
     public function setXmlValue(array $value): void
     {
-        $value = array_map('floatval', $value);
+        $value = array_map(floatval(...), $value);
         parent::setXmlValue($value);
     }
 
@@ -101,7 +101,7 @@ protected function xmlSerializeValue(Xml\Writer $writer): void
         // See:
         // http://tools.ietf.org/html/rfc6321#section-3.4.1.2
         if ('GEO' === $this->name) {
-            $value = array_map('floatval', $this->getParts());
+            $value = array_map(floatval(...), $this->getParts());
 
             $writer->writeElement('latitude', $value[0]);
             $writer->writeElement('longitude', $value[1]);
diff --git a/lib/Property/ICalendar/CalAddress.php b/lib/Property/ICalendar/CalAddress.php
index 01969e87d..a2b13eee7 100644
--- a/lib/Property/ICalendar/CalAddress.php
+++ b/lib/Property/ICalendar/CalAddress.php
@@ -43,10 +43,10 @@ public function getValueType(): string
     public function getNormalizedValue(): string
     {
         $input = $this->getValue();
-        if (!strpos($input, ':')) {
+        if (!strpos((string) $input, ':')) {
             return $input;
         }
-        list($schema, $everythingElse) = explode(':', $input, 2);
+        [$schema, $everythingElse] = explode(':', (string) $input, 2);
         $schema = strtolower($schema);
         if ('mailto' === $schema) {
             $everythingElse = strtolower($everythingElse);
diff --git a/lib/Property/ICalendar/DateTime.php b/lib/Property/ICalendar/DateTime.php
index 4f2ff4261..cd92475f3 100644
--- a/lib/Property/ICalendar/DateTime.php
+++ b/lib/Property/ICalendar/DateTime.php
@@ -111,7 +111,7 @@ public function isFloating(): bool
             !$this->hasTime()
             || (
                 !isset($this['TZID'])
-                && false === strpos($this->getValue(), 'Z')
+                && !str_contains((string) $this->getValue(), 'Z')
             );
     }
 
@@ -205,7 +205,7 @@ public function setDateTimes(array $dt, $isFloating = false): void
                 }
                 if (is_null($tz)) {
                     $tz = $d->getTimeZone();
-                    $isUtc = in_array($tz->getName(), ['UTC', 'GMT', 'Z', '+00:00']);
+                    $isUtc = in_array($tz->getName(), ['UTC', 'GMT', 'Z', '+00:00'], true);
                     if (!$isUtc) {
                         $this->offsetSet('TZID', $tz->getName());
                     }
@@ -257,7 +257,7 @@ public function getJsonValue(): array
         $isFloating = $this->isFloating();
 
         $tz = $dts[0]->getTimeZone();
-        $isUtc = !$isFloating && in_array($tz->getName(), ['UTC', 'GMT', 'Z']);
+        $isUtc = !$isFloating && in_array($tz->getName(), ['UTC', 'GMT', 'Z'], true);
 
         return array_map(
             function (\DateTimeInterface $dt) use ($hasTime, $isUtc) {
@@ -286,9 +286,7 @@ public function setJsonValue(array $value): void
         // those.
         $this->setValue(
             array_map(
-                function ($item) {
-                    return strtr($item, [':' => '', '-' => '']);
-                },
+                fn ($item) => strtr($item, [':' => '', '-' => '']),
                 $value
             )
         );
@@ -306,7 +304,7 @@ function ($item) {
     public function offsetSet($offset, $value): void
     {
         parent::offsetSet($offset, $value);
-        if ('VALUE' !== strtoupper($offset)) {
+        if ('VALUE' !== strtoupper((string) $offset)) {
             return;
         }
 
@@ -347,7 +345,7 @@ public function validate(int $options = 0): array
                         DateTimeParser::parseDateTime($value);
                         break;
                 }
-            } catch (InvalidDataException $e) {
+            } catch (InvalidDataException) {
                 $messages[] = [
                     'level' => 3,
                     'message' => 'The supplied value ('.$value.') is not a correct '.$valueType,
diff --git a/lib/Property/ICalendar/Period.php b/lib/Property/ICalendar/Period.php
index 7632cb4d1..15291e805 100644
--- a/lib/Property/ICalendar/Period.php
+++ b/lib/Property/ICalendar/Period.php
@@ -64,9 +64,7 @@ public function getValueType(): string
     public function setJsonValue(array $value): void
     {
         $value = array_map(
-            function ($item) {
-                return strtr(implode('/', $item), [':' => '', '-' => '']);
-            },
+            fn ($item) => strtr(implode('/', $item), [':' => '', '-' => '']),
             $value
         );
         parent::setJsonValue($value);
@@ -83,7 +81,7 @@ public function getJsonValue(): array
     {
         $return = [];
         foreach ($this->getParts() as $item) {
-            list($start, $end) = explode('/', $item, 2);
+            [$start, $end] = explode('/', (string) $item, 2);
 
             $start = DateTimeParser::parseDateTime($start);
 
diff --git a/lib/Property/ICalendar/Recur.php b/lib/Property/ICalendar/Recur.php
index 10081673e..f3d45158a 100644
--- a/lib/Property/ICalendar/Recur.php
+++ b/lib/Property/ICalendar/Recur.php
@@ -29,14 +29,14 @@ class Recur extends Property
     /**
      * Reference to the parent object, if this is not the top object.
      */
-    public ?Node $parent;
+    public ?Node $parent = null;
 
     /**
      * Updates the current value.
      *
      * This may be either a single, or multiple strings in an array.
      *
-     * @param string|array $value
+     * @param string|array|object $value
      */
     public function setValue($value): void
     {
@@ -52,17 +52,17 @@ public function setValue($value): void
                     $v = strtoupper($v);
 
                     // The value had multiple sub-values
-                    if (false !== strpos($v, ',')) {
+                    if (str_contains($v, ',')) {
                         $v = explode(',', $v);
                     }
-                    if (0 === strcmp($k, 'until')) {
+                    if (0 === strcmp((string) $k, 'until')) {
                         $v = strtr($v, [':' => '', '-' => '']);
                     }
                 } elseif (is_array($v)) {
-                    $v = array_map('strtoupper', $v);
+                    $v = array_map(strtoupper(...), $v);
                 }
 
-                $newVal[strtoupper($k)] = $v;
+                $newVal[strtoupper((string) $k)] = $v;
             }
             $this->value = $newVal;
         } elseif (is_string($value)) {
@@ -151,13 +151,13 @@ public function getJsonValue(): array
     {
         $values = [];
         foreach ($this->getParts() as $k => $v) {
-            if (0 === strcmp($k, 'UNTIL')) {
+            if (0 === strcmp((string) $k, 'UNTIL')) {
                 $date = new DateTime($this->root, null, $v);
-                $values[strtolower($k)] = $date->getJsonValue()[0];
-            } elseif (0 === strcmp($k, 'COUNT')) {
-                $values[strtolower($k)] = intval($v);
+                $values[strtolower((string) $k)] = $date->getJsonValue()[0];
+            } elseif (0 === strcmp((string) $k, 'COUNT')) {
+                $values[strtolower((string) $k)] = intval($v);
             } else {
-                $values[strtolower($k)] = $v;
+                $values[strtolower((string) $k)] = $v;
             }
         }
 
@@ -186,7 +186,7 @@ public static function stringToArray(string $value): array
         $newValue = [];
         foreach (explode(';', $value) as $part) {
             // Skipping empty parts.
-            if (empty($part)) {
+            if ('' === $part) {
                 continue;
             }
 
@@ -196,10 +196,10 @@ public static function stringToArray(string $value): array
                 throw new InvalidDataException('The supplied iCalendar RRULE part is incorrect: '.$part);
             }
 
-            list($partName, $partValue) = $parts;
+            [$partName, $partValue] = $parts;
 
             // The value itself had multiple values..
-            if (false !== strpos($partValue, ',')) {
+            if (str_contains($partValue, ',')) {
                 $partValue = explode(',', $partValue);
             }
             $newValue[$partName] = $partValue;
@@ -243,7 +243,7 @@ public function validate(int $options = 0): array
                 if ($repair) {
                     unset($values[$key]);
                 }
-            } elseif ('BYMONTH' == $key) {
+            } elseif ('BYMONTH' === $key) {
                 $byMonth = (array) $value;
                 foreach ($byMonth as $i => $v) {
                     if (!is_numeric($v) || (int) $v < 1 || (int) $v > 12) {
@@ -262,13 +262,13 @@ public function validate(int $options = 0): array
                     }
                 }
                 // if there is no valid entry left, remove the whole value
-                if (is_array($value) && empty($values[$key])) {
+                if (is_array($value) && ([] === $values[$key])) {
                     unset($values[$key]);
                 }
-            } elseif ('BYWEEKNO' == $key) {
+            } elseif ('BYWEEKNO' === $key) {
                 $byWeekNo = (array) $value;
                 foreach ($byWeekNo as $i => $v) {
-                    if (!is_numeric($v) || (int) $v < -53 || 0 == (int) $v || (int) $v > 53) {
+                    if (!is_numeric($v) || (int) $v < -53 || 0 === (int) $v || (int) $v > 53) {
                         $warnings[] = [
                             'level' => $repair ? 1 : 3,
                             'message' => 'BYWEEKNO in RRULE must have value(s) from -53 to -1, or 1 to 53!',
@@ -284,13 +284,13 @@ public function validate(int $options = 0): array
                     }
                 }
                 // if there is no valid entry left, remove the whole value
-                if (is_array($value) && empty($values[$key])) {
+                if (is_array($value) && ([] === $values[$key])) {
                     unset($values[$key]);
                 }
-            } elseif ('BYYEARDAY' == $key) {
+            } elseif ('BYYEARDAY' === $key) {
                 $byYearDay = (array) $value;
                 foreach ($byYearDay as $i => $v) {
-                    if (!is_numeric($v) || (int) $v < -366 || 0 == (int) $v || (int) $v > 366) {
+                    if (!is_numeric($v) || (int) $v < -366 || 0 === (int) $v || (int) $v > 366) {
                         $warnings[] = [
                             'level' => $repair ? 1 : 3,
                             'message' => 'BYYEARDAY in RRULE must have value(s) from -366 to -1, or 1 to 366!',
@@ -306,7 +306,7 @@ public function validate(int $options = 0): array
                     }
                 }
                 // if there is no valid entry left, remove the whole value
-                if (is_array($value) && empty($values[$key])) {
+                if (is_array($value) && ([] === $values[$key])) {
                     unset($values[$key]);
                 }
             }
diff --git a/lib/Property/IntegerValue.php b/lib/Property/IntegerValue.php
index f1ae55d17..1cd7273cc 100644
--- a/lib/Property/IntegerValue.php
+++ b/lib/Property/IntegerValue.php
@@ -62,7 +62,7 @@ public function getJsonValue(): array
      */
     public function setXmlValue(array $value): void
     {
-        $value = array_map('intval', $value);
+        $value = array_map(intval(...), $value);
         parent::setXmlValue($value);
     }
 }
diff --git a/lib/Property/Text.php b/lib/Property/Text.php
index 363c3fa4f..e585026fc 100644
--- a/lib/Property/Text.php
+++ b/lib/Property/Text.php
@@ -71,7 +71,7 @@ public function __construct(Component $root, string $name, $value = null, array
         // 2. structured value properties
         //
         // The former is always separated by a comma, the latter by semicolon.
-        if (in_array($name, $this->structuredValues)) {
+        if (in_array($name, $this->structuredValues, true)) {
             $this->delimiter = ';';
         }
 
@@ -155,7 +155,7 @@ public function getJsonValue(): array
         // Structured text values should always be returned as a single
         // array-item. Multi-value text should be returned as multiple items in
         // the top-array.
-        if (in_array($this->name, $this->structuredValues)) {
+        if (in_array($this->name, $this->structuredValues, true)) {
             return [$this->getParts()];
         }
 
@@ -213,7 +213,7 @@ public function serialize(): string
 
         // If the resulting value contains a \n, we must encode it as
         // quoted-printable.
-        if (false !== \strpos($val, "\n")) {
+        if (str_contains((string) $val, "\n")) {
             $str .= ';ENCODING=QUOTED-PRINTABLE:';
             $lastLine = $str;
             $out = '';
@@ -222,13 +222,13 @@ public function serialize(): string
             // encode newlines for us. Specifically, the \r\n sequence must in
             // vcards be encoded as =0D=OA and we must insert soft-newlines
             // every 75 bytes.
-            for ($ii = 0; $ii < \strlen($val); ++$ii) {
+            for ($ii = 0; $ii < \strlen((string) $val); ++$ii) {
                 $ord = \ord($val[$ii]);
                 // These characters are encoded as themselves.
                 if ($ord >= 32 && $ord <= 126) {
                     $lastLine .= $val[$ii];
                 } else {
-                    $lastLine .= '='.\strtoupper(\bin2hex($val[$ii]));
+                    $lastLine .= '='.\strtoupper(\bin2hex((string) $val[$ii]));
                 }
                 if (\strlen($lastLine) >= 75) {
                     // Soft line break
@@ -255,7 +255,7 @@ public function serialize(): string
         );
 
         // remove single space after last CRLF
-        return \substr($str, 0, -1);
+        return \substr((string) $str, 0, -1);
     }
 
     /**
@@ -270,7 +270,7 @@ protected function xmlSerializeValue(Xml\Writer $writer): void
             foreach ($items as $i => $item) {
                 $writer->writeElement(
                     $item,
-                    !empty($values[$i]) ? $values[$i] : null
+                    ('' !== $values[$i] && [] !== $values[$i]) ? $values[$i] : null
                 );
             }
         };
diff --git a/lib/Property/Time.php b/lib/Property/Time.php
index ed314fc0d..9c4016c64 100644
--- a/lib/Property/Time.php
+++ b/lib/Property/Time.php
@@ -104,7 +104,7 @@ public function getJsonValue(): array
                 $timeStr .= 'Z';
             } else {
                 $timeStr .=
-                    preg_replace('/([0-9]{2})([0-9]{2})$/', '$1:$2', $parts['timezone']);
+                    preg_replace('/([0-9]{2})([0-9]{2})$/', '$1:$2', (string) $parts['timezone']);
             }
         }
 
@@ -118,9 +118,7 @@ public function getJsonValue(): array
     public function setXmlValue(array $value): void
     {
         $value = array_map(
-            function ($value) {
-                return str_replace(':', '', $value);
-            },
+            fn ($value) => str_replace(':', '', $value),
             $value
         );
         parent::setXmlValue($value);
diff --git a/lib/Property/Uri.php b/lib/Property/Uri.php
index 228b7090f..dce7bf4bb 100644
--- a/lib/Property/Uri.php
+++ b/lib/Property/Uri.php
@@ -38,7 +38,7 @@ public function getValueType(): string
     public function parameters(): array
     {
         $parameters = parent::parameters();
-        if (!isset($parameters['VALUE']) && in_array($this->name, ['URL', 'PHOTO'])) {
+        if (!isset($parameters['VALUE']) && in_array($this->name, ['URL', 'PHOTO'], true)) {
             // If we are encoding a URI value, and this URI value has no
             // VALUE=URI parameter, we add it anyway.
             //
@@ -74,14 +74,10 @@ public function setRawMimeDirValue(string $val): void
             $matches = preg_split($regex, $val, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);
             $newVal = '';
             foreach ($matches as $match) {
-                switch ($match) {
-                    case '\:':
-                        $newVal .= ':';
-                        break;
-                    default:
-                        $newVal .= $match;
-                        break;
-                }
+                match ($match) {
+                    '\:' => $newVal .= ':',
+                    default => $newVal .= $match,
+                };
             }
             $this->value = $newVal;
         } else {
diff --git a/lib/Property/UtcOffset.php b/lib/Property/UtcOffset.php
index 09aab0151..52d81f1f6 100644
--- a/lib/Property/UtcOffset.php
+++ b/lib/Property/UtcOffset.php
@@ -42,9 +42,7 @@ public function getValueType(): string
     public function setJsonValue(array $value): void
     {
         $value = array_map(
-            function ($value) {
-                return str_replace(':', '', $value);
-            },
+            fn ($value) => str_replace(':', '', $value),
             $value
         );
         parent::setJsonValue($value);
@@ -58,10 +56,8 @@ function ($value) {
     public function getJsonValue(): array
     {
         return array_map(
-            function ($value) {
-                return substr($value, 0, -2).':'.
-                       substr($value, -2);
-            },
+            fn ($value) => substr((string) $value, 0, -2).':'.
+                   substr((string) $value, -2),
             parent::getJsonValue()
         );
     }
diff --git a/lib/Property/VCard/DateAndOrTime.php b/lib/Property/VCard/DateAndOrTime.php
index e87bf1b3a..9a7693961 100644
--- a/lib/Property/VCard/DateAndOrTime.php
+++ b/lib/Property/VCard/DateAndOrTime.php
@@ -77,7 +77,7 @@ public function setValue($value): void
     public function setDateTime(\DateTimeInterface $dt): void
     {
         $tz = $dt->getTimeZone();
-        $isUtc = in_array($tz->getName(), ['UTC', 'GMT', 'Z']);
+        $isUtc = in_array($tz->getName(), ['UTC', 'GMT', 'Z'], true);
 
         if ($isUtc) {
             $value = $dt->format('Ymd\\THis\\Z');
@@ -232,14 +232,10 @@ protected function xmlSerializeValue(Xml\Writer $writer): void
         $value = '';
 
         // $d = defined
-        $d = function ($part) use ($parts): bool {
-            return !is_null($parts[$part]);
-        };
+        $d = (fn ($part): bool => !is_null($parts[$part]));
 
         // $r = read
-        $r = function ($part) use ($parts) {
-            return $parts[$part];
-        };
+        $r = (fn ($part) => $parts[$part]);
 
         // From the Relax NG Schema.
         //
@@ -341,7 +337,7 @@ public function validate(int $options = 0): array
 
         try {
             DateTimeParser::parseVCardDateTime($value);
-        } catch (InvalidDataException $e) {
+        } catch (InvalidDataException) {
             $messages[] = [
                 'level' => 3,
                 'message' => 'The supplied value ('.$value.') is not a correct DATE-AND-OR-TIME property',
diff --git a/lib/Recur/RDateIterator.php b/lib/Recur/RDateIterator.php
index 4ad688f9d..b9bd0beff 100644
--- a/lib/Recur/RDateIterator.php
+++ b/lib/Recur/RDateIterator.php
@@ -26,9 +26,13 @@ class RDateIterator implements \Iterator
      *
      * @param string|array $rrule
      */
-    public function __construct($rrule, \DateTimeInterface $start)
+    public function __construct($rrule, /**
+     * The reference start date/time for the rrule.
+     *
+     * All calculations are based on this initial date.
+     */
+        protected \DateTimeInterface $startDate)
     {
-        $this->startDate = $start;
         $this->parseRDate($rrule);
         $this->currentDate = clone $this->startDate;
     }
@@ -117,13 +121,6 @@ public function fastForward(\DateTimeInterface $dt): void
         }
     }
 
-    /**
-     * The reference start date/time for the rrule.
-     *
-     * All calculations are based on this initial date.
-     */
-    protected \DateTimeInterface $startDate;
-
     /**
      * The date of the current iteration. You can get this by calling
      * ->current().
diff --git a/lib/Recur/RRuleIterator.php b/lib/Recur/RRuleIterator.php
index 87e185b1c..de1c123b5 100644
--- a/lib/Recur/RRuleIterator.php
+++ b/lib/Recur/RRuleIterator.php
@@ -37,9 +37,13 @@ class RRuleIterator implements \Iterator
      *
      * @throws InvalidDataException
      */
-    public function __construct($rrule, \DateTimeInterface $start)
+    public function __construct($rrule, /**
+     * The reference start date/time for the rrule.
+     *
+     * All calculations are based on this initial date.
+     */
+        protected \DateTimeInterface $startDate)
     {
-        $this->startDate = $start;
         $this->parseRRule($rrule);
         $this->currentDate = clone $this->startDate;
     }
@@ -146,13 +150,6 @@ public function fastForward(\DateTimeInterface $dt): void
         }
     }
 
-    /**
-     * The reference start date/time for the rrule.
-     *
-     * All calculations are based on this initial date.
-     */
-    protected \DateTimeInterface $startDate;
-
     /**
      * The date of the current iteration. You can get this by calling
      * ->current().
@@ -357,23 +354,23 @@ protected function nextDaily(): void
         }
 
         $recurrenceHours = [];
-        if (!empty($this->byHour)) {
+        if ($this->byHour) {
             $recurrenceHours = $this->getHours();
         }
 
         $recurrenceDays = [];
-        if (!empty($this->byDay)) {
+        if ($this->byDay) {
             $recurrenceDays = $this->getDays();
         }
 
         $recurrenceMonths = [];
-        if (!empty($this->byMonth)) {
+        if ($this->byMonth) {
             $recurrenceMonths = $this->getMonths();
         }
 
         do {
             if ($this->byHour) {
-                if ('23' == $this->currentDate->format('G')) {
+                if ('23' === $this->currentDate->format('G')) {
                     // to obey the interval rule
                     $this->currentDate = $this->currentDate->modify('+'.($this->interval - 1).' days');
                 }
@@ -398,9 +395,9 @@ protected function nextDaily(): void
                 return;
             }
         } while (
-            ($this->byDay && !in_array($currentDay, $recurrenceDays))
-            || ($this->byHour && !in_array($currentHour, $recurrenceHours))
-            || ($this->byMonth && !in_array($currentMonth, $recurrenceMonths))
+            ($this->byDay && !in_array((int) $currentDay, $recurrenceDays, true))
+            || ($this->byHour && !in_array($currentHour, $recurrenceHours, true))
+            || ($this->byMonth && !in_array($currentMonth, $recurrenceMonths, true))
         );
     }
 
@@ -442,18 +439,18 @@ protected function nextWeekly(): void
             $currentHour = (int) $this->currentDate->format('G');
 
             // We need to roll over to the next week
-            if ($currentDay === $firstDay && (!$this->byHour || '0' == $currentHour)) {
+            if ($currentDay === $firstDay && (!$this->byHour || 0 === $currentHour)) {
                 $this->currentDate = $this->currentDate->modify('+'.($this->interval - 1).' weeks');
 
                 // We need to go to the first day of this week, but only if we
                 // are not already on this first day of this week.
-                if ($this->currentDate->format('w') != $firstDay) {
+                if ((int) $this->currentDate->format('w') !== $firstDay) {
                     $this->currentDate = $this->currentDate->modify('last '.$this->dayNames[$this->dayMap[$this->weekStart]]);
                 }
             }
 
             // We have a match
-        } while (($this->byDay && !in_array($currentDay, $recurrenceDays)) || ($this->byHour && !in_array($currentHour, $recurrenceHours)));
+        } while (($this->byDay && !in_array($currentDay, $recurrenceDays, true)) || ($this->byHour && !in_array((string) $currentHour, $recurrenceHours, true)));
     }
 
     /**
@@ -476,14 +473,14 @@ protected function nextMonthly(): void
                     ++$increase;
                     $tempDate = clone $this->currentDate;
                     $tempDate = $tempDate->modify('+ '.($this->interval * $increase).' months '.$this->startTime());
-                } while ($tempDate->format('j') != $currentDayOfMonth);
+                } while ($tempDate->format('j') !== $currentDayOfMonth);
                 $this->currentDate = $tempDate;
             }
 
             return;
         }
 
-        $occurrence = -1;
+        $selectedOccurrence = -1;
         while (true) {
             $occurrences = $this->getMonthlyOccurrences();
 
@@ -491,6 +488,7 @@ protected function nextMonthly(): void
                 // The first occurrence that's higher than the current
                 // day of the month wins.
                 if ($occurrence > $currentDayOfMonth) {
+                    $selectedOccurrence = $occurrence;
                     break 2;
                 }
             }
@@ -533,7 +531,7 @@ protected function nextMonthly(): void
         $this->currentDate = $this->currentDate->setDate(
             (int) $this->currentDate->format('Y'),
             (int) $this->currentDate->format('n'),
-            (int) $occurrence
+            (int) $selectedOccurrence
         )->modify($this->startTime());
     }
 
@@ -547,9 +545,9 @@ protected function nextYearly(): void
         $currentDayOfMonth = $this->currentDate->format('j');
 
         // No sub-rules, so we just advance by year
-        if (empty($this->byMonth)) {
+        if (!$this->byMonth) {
             // Unless it was a leap day!
-            if (2 == $currentMonth && 29 == $currentDayOfMonth) {
+            if (2 === (int) $currentMonth && 29 === (int) $currentDayOfMonth) {
                 $counter = 0;
                 do {
                     ++$counter;
@@ -563,7 +561,7 @@ protected function nextYearly(): void
                     // functions instead.
                     $nextDate = clone $this->currentDate;
                     $nextDate = $nextDate->modify('+ '.($this->interval * $counter).' years');
-                } while (2 != $nextDate->format('n'));
+                } while (2 !== (int) $nextDate->format('n'));
 
                 $this->currentDate = $nextDate;
 
@@ -634,7 +632,7 @@ protected function nextYearly(): void
                             $date = $date->sub(new \DateInterval('P'.abs($byYearDay + 1).'D'));
                         }
 
-                        if ($date > $this->currentDate && in_array($date->format('N'), $dayOffsets)) {
+                        if ($date > $this->currentDate && in_array((int) $date->format('N'), $dayOffsets, true)) {
                             $checkDates[] = $date;
                         }
                     }
@@ -665,7 +663,7 @@ protected function nextYearly(): void
         // If we got a byDay or getMonthDay filter, we must first expand
         // further.
         if ($this->byDay || $this->byMonthDay) {
-            $occurrence = -1;
+            $selectedOccurrence = -1;
             while (true) {
                 $occurrences = $this->getMonthlyOccurrences();
 
@@ -677,7 +675,8 @@ protected function nextYearly(): void
                     if ($occurrence > $currentDayOfMonth || $advancedToNewMonth) {
                         // only consider byMonth matches,
                         // otherwise, we don't follow RRule correctly
-                        if (in_array($currentMonth, $this->byMonth)) {
+                        if (in_array((string) $currentMonth, $this->byMonth, true)) {
+                            $selectedOccurrence = $occurrence;
                             break 2;
                         }
                     }
@@ -693,12 +692,12 @@ protected function nextYearly(): void
                         $currentYear += $this->interval;
                         $currentMonth = 1;
                     }
-                } while (!in_array($currentMonth, $this->byMonth));
+                } while (!in_array((string) $currentMonth, $this->byMonth, true));
 
                 $this->currentDate = $this->currentDate->setDate(
                     (int) $currentYear,
-                    (int) $currentMonth,
-                    (int) $currentDayOfMonth
+                    $currentMonth,
+                    $currentDayOfMonth
                 );
 
                 // To prevent running this forever (better: until we hit the max date of DateTimeImmutable) we simply
@@ -714,7 +713,7 @@ protected function nextYearly(): void
             $this->currentDate = $this->currentDate->setDate(
                 (int) $currentYear,
                 (int) $currentMonth,
-                (int) $occurrence
+                (int) $selectedOccurrence
             )->modify($this->startTime());
 
             return;
@@ -727,10 +726,10 @@ protected function nextYearly(): void
                 $currentYear += $this->interval;
                 $currentMonth = 1;
             }
-        } while (!in_array($currentMonth, $this->byMonth));
+        } while (!in_array((string) $currentMonth, $this->byMonth, true));
         $this->currentDate = $this->currentDate->setDate(
             (int) $currentYear,
-            (int) $currentMonth,
+            $currentMonth,
             (int) $currentDayOfMonth
         )->modify($this->startTime());
     }
@@ -752,13 +751,14 @@ protected function parseRRule($rrule): void
         }
 
         foreach ($rrule as $key => $value) {
-            $key = strtoupper($key);
+            $key = strtoupper((string) $key);
             switch ($key) {
                 case 'FREQ':
-                    $value = strtolower($value);
+                    $value = strtolower((string) $value);
                     if (!in_array(
                         $value,
-                        ['secondly', 'minutely', 'hourly', 'daily', 'weekly', 'monthly', 'yearly']
+                        ['secondly', 'minutely', 'hourly', 'daily', 'weekly', 'monthly', 'yearly'],
+                        true
                     )) {
                         throw new InvalidDataException('Unknown value for FREQ='.strtoupper($value));
                     }
@@ -806,7 +806,7 @@ protected function parseRRule($rrule): void
                 case 'BYDAY':
                     $value = (array) $value;
                     foreach ($value as $part) {
-                        if (!preg_match('#^  (-|\+)? ([1-5])? (MO|TU|WE|TH|FR|SA|SU) $# xi', $part)) {
+                        if (!preg_match('#^  (-|\+)? ([1-5])? (MO|TU|WE|TH|FR|SA|SU) $# xi', (string) $part)) {
                             throw new InvalidDataException('Invalid part in BYDAY clause: '.$part);
                         }
                     }
@@ -820,7 +820,7 @@ protected function parseRRule($rrule): void
                 case 'BYYEARDAY':
                     $this->byYearDay = (array) $value;
                     foreach ($this->byYearDay as $byYearDay) {
-                        if (!is_numeric($byYearDay) || (int) $byYearDay < -366 || 0 == (int) $byYearDay || (int) $byYearDay > 366) {
+                        if (!is_numeric($byYearDay) || (int) $byYearDay < -366 || 0 === (int) $byYearDay || (int) $byYearDay > 366) {
                             throw new InvalidDataException('BYYEARDAY in RRULE must have value(s) from 1 to 366, or -366 to -1!');
                         }
                     }
@@ -829,7 +829,7 @@ protected function parseRRule($rrule): void
                 case 'BYWEEKNO':
                     $this->byWeekNo = (array) $value;
                     foreach ($this->byWeekNo as $byWeekNo) {
-                        if (!is_numeric($byWeekNo) || (int) $byWeekNo < -53 || 0 == (int) $byWeekNo || (int) $byWeekNo > 53) {
+                        if (!is_numeric($byWeekNo) || (int) $byWeekNo < -53 || 0 === (int) $byWeekNo || (int) $byWeekNo > 53) {
                             throw new InvalidDataException('BYWEEKNO in RRULE must have value(s) from 1 to 53, or -53 to -1!');
                         }
                     }
@@ -849,7 +849,7 @@ protected function parseRRule($rrule): void
                     break;
 
                 case 'WKST':
-                    $this->weekStart = strtoupper($value);
+                    $this->weekStart = strtoupper((string) $value);
                     break;
 
                 default:
@@ -889,7 +889,7 @@ protected function getMonthlyOccurrences(): array
         // that point and add it to the results.
         if ($this->byDay) {
             foreach ($this->byDay as $day) {
-                $dayName = $this->dayNames[$this->dayMap[substr($day, -2)]];
+                $dayName = $this->dayNames[$this->dayMap[substr((string) $day, -2)]];
 
                 // Dayname will be something like 'wednesday'. Now we need to find
                 // all wednesdays in this month.
@@ -910,8 +910,8 @@ protected function getMonthlyOccurrences(): array
                 // So now we have 'all wednesdays' for month. It is however
                 // possible that the user only really wanted the 1st, 2nd or last
                 // wednesday.
-                if (strlen($day) > 2) {
-                    $offset = (int) substr($day, 0, -2);
+                if (strlen((string) $day) > 2) {
+                    $offset = (int) substr((string) $day, 0, -2);
 
                     if ($offset > 0) {
                         // It is possible that the day does not exist, such as a
@@ -1015,7 +1015,7 @@ protected function getDays(): array
             // The day may be preceded with a positive (+n) or
             // negative (-n) integer. However, this does not make
             // sense in 'weekly' so we ignore it here.
-            $recurrenceDays[] = $this->dayMap[substr($byDay, -2)];
+            $recurrenceDays[] = $this->dayMap[substr((string) $byDay, -2)];
         }
 
         return $recurrenceDays;
diff --git a/lib/Splitter/VCard.php b/lib/Splitter/VCard.php
index 40775a335..a802dbe75 100644
--- a/lib/Splitter/VCard.php
+++ b/lib/Splitter/VCard.php
@@ -22,13 +22,6 @@
  */
 class VCard implements SplitterInterface
 {
-    /**
-     * File handle.
-     *
-     * @var resource
-     */
-    protected $input;
-
     /**
      * Persistent parser.
      */
@@ -42,10 +35,12 @@ class VCard implements SplitterInterface
      * @param resource $input
      * @param int      $options parser options, see the OPTIONS constants
      */
-    public function __construct($input, int $options = 0)
+    public function __construct(/**
+     * File handle.
+     */
+        protected $input, int $options = 0)
     {
-        $this->input = $input;
-        $this->parser = new MimeDir($input, $options);
+        $this->parser = new MimeDir($this->input, $options);
     }
 
     /**
@@ -64,7 +59,7 @@ public function getNext(): ?Component
             if (!$object instanceof Component\VCard) {
                 throw new VObject\ParseException('The supplied input contained non-VCARD data.');
             }
-        } catch (VObject\EofException $e) {
+        } catch (VObject\EofException) {
             return null;
         }
 
diff --git a/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
index ba84d45eb..5e56b82f1 100644
--- a/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
+++ b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
@@ -40,13 +40,13 @@ public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZo
 
         try {
             if (
-                in_array($tzid, $tzIdentifiers)
+                in_array($tzid, $tzIdentifiers, true)
                 || preg_match('/^GMT(\+|-)([0-9]{4})$/', $tzid, $matches)
-                || in_array($tzid, $this->getIdentifiersBC())
+                || in_array($tzid, $this->getIdentifiersBC(), true)
             ) {
                 return new \DateTimeZone($tzid);
             }
-        } catch (\Exception $e) {
+        } catch (\Exception) {
         }
 
         return null;
diff --git a/lib/TimezoneGuesser/FindFromTimezoneMap.php b/lib/TimezoneGuesser/FindFromTimezoneMap.php
index f203937bc..5beb5450d 100644
--- a/lib/TimezoneGuesser/FindFromTimezoneMap.php
+++ b/lib/TimezoneGuesser/FindFromTimezoneMap.php
@@ -27,7 +27,7 @@ public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZo
         if ($this->hasTzInMap($tzid)) {
             try {
                 return new \DateTimeZone($this->getTzFromMap($tzid));
-            } catch (\Exception $e) {
+            } catch (\Exception) {
                 return null;
             }
         }
@@ -43,7 +43,7 @@ public function find(string $tzid, ?bool $failIfUncertain = false): ?\DateTimeZo
             if ($this->hasTzInMap($tzidAlternate)) {
                 try {
                     return new \DateTimeZone($this->getTzFromMap($tzidAlternate));
-                } catch (\Exception $e) {
+                } catch (\Exception) {
                     return null;
                 }
             }
diff --git a/lib/TimezoneGuesser/GuessFromLicEntry.php b/lib/TimezoneGuesser/GuessFromLicEntry.php
index 486b33796..7212117f7 100644
--- a/lib/TimezoneGuesser/GuessFromLicEntry.php
+++ b/lib/TimezoneGuesser/GuessFromLicEntry.php
@@ -23,7 +23,7 @@ public function guess(VTimeZone $vtimezone, ?bool $failIfUncertain = false): ?\D
         // Libical generators may specify strings like
         // "SystemV/EST5EDT". For those we must remove the
         // SystemV part.
-        if ('SystemV/' === substr($lic, 0, 8)) {
+        if (str_starts_with($lic, 'SystemV/')) {
             $lic = substr($lic, 8);
         }
 
diff --git a/lib/TimezoneGuesser/GuessFromMsTzId.php b/lib/TimezoneGuesser/GuessFromMsTzId.php
index 392333cb0..82060bd27 100644
--- a/lib/TimezoneGuesser/GuessFromMsTzId.php
+++ b/lib/TimezoneGuesser/GuessFromMsTzId.php
@@ -105,7 +105,7 @@ public function guess(VTimeZone $vtimezone, ?bool $failIfUncertain = false): ?\D
         $cdoId = (int) $vtimezone->{'X-MICROSOFT-CDO-TZID'}->getValue();
 
         // 2 can mean both Europe/Lisbon and Europe/Sarajevo.
-        if (2 === $cdoId && false !== strpos((string) $vtimezone->TZID, 'Sarajevo')) {
+        if (2 === $cdoId && str_contains((string) $vtimezone->TZID, 'Sarajevo')) {
             return new \DateTimeZone('Europe/Sarajevo');
         }
 
diff --git a/lib/VCardConverter.php b/lib/VCardConverter.php
index ff8fe3f81..39969d558 100644
--- a/lib/VCardConverter.php
+++ b/lib/VCardConverter.php
@@ -38,10 +38,10 @@ public function convert(Component\VCard $input, int $targetVersion): Component\V
             return clone $input;
         }
 
-        if (!in_array($inputVersion, [Document::VCARD21, Document::VCARD30, Document::VCARD40])) {
+        if (!in_array($inputVersion, [Document::VCARD21, Document::VCARD30, Document::VCARD40], true)) {
             throw new \InvalidArgumentException('Only vCard 2.1, 3.0 and 4.0 are supported for the input data');
         }
-        if (!in_array($targetVersion, [Document::VCARD30, Document::VCARD40])) {
+        if (!in_array($targetVersion, [Document::VCARD30, Document::VCARD40], true)) {
             throw new \InvalidArgumentException('You can only use vCard 3.0 or 4.0 for the target version');
         }
 
@@ -69,7 +69,7 @@ public function convert(Component\VCard $input, int $targetVersion): Component\V
     protected function convertProperty(Component\VCard $input, Component\VCard $output, Property $property, int $targetVersion): void
     {
         // Skipping these, those are automatically added.
-        if (in_array($property->name, ['VERSION', 'PRODID'])) {
+        if (in_array($property->name, ['VERSION', 'PRODID'], true)) {
             return;
         }
 
@@ -93,7 +93,7 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
         );
 
         if (Document::VCARD30 === $targetVersion) {
-            if ($property instanceof Uri && in_array($property->name, ['PHOTO', 'LOGO', 'SOUND'])) {
+            if ($property instanceof Uri && in_array($property->name, ['PHOTO', 'LOGO', 'SOUND'], true)) {
                 /** @var Uri $newProperty */
                 $newProperty = $this->convertUriToBinary($output, $newProperty);
             } elseif ($property instanceof Property\VCard\DateAndOrTime) {
@@ -111,7 +111,7 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
                     $newProperty['X-APPLE-OMIT-YEAR'] = '1604';
                 }
 
-                if ('ANNIVERSARY' == $newProperty->name) {
+                if ('ANNIVERSARY' === $newProperty->name) {
                     // Microsoft non-standard anniversary
                     $newProperty->name = 'X-ANNIVERSARY';
 
@@ -127,7 +127,7 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
                     $output->add('ITEM'.$x.'.X-ABLABEL', '_$!<Anniversary>!$_');
                 }
             } elseif ('KIND' === $property->name) {
-                switch (strtolower($property->getValue())) {
+                switch (strtolower((string) $property->getValue())) {
                     case 'org':
                         // vCard 3.0 does not have an equivalent to KIND:ORG,
                         // but apple has an extension that means the same
@@ -149,7 +149,7 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
             }
         } elseif (Document::VCARD40 === $targetVersion) {
             // These properties were removed in vCard 4.0
-            if (in_array($property->name, ['NAME', 'MAILER', 'LABEL', 'CLASS'])) {
+            if (in_array($property->name, ['NAME', 'MAILER', 'LABEL', 'CLASS'], true)) {
                 return;
             }
 
@@ -171,12 +171,12 @@ protected function convertProperty(Component\VCard $input, Component\VCard $outp
             }
             switch ($property->name) {
                 case 'X-ABSHOWAS':
-                    if ('COMPANY' === strtoupper($property->getValue())) {
+                    if ('COMPANY' === strtoupper((string) $property->getValue())) {
                         $newProperty = $output->createProperty('KIND', 'ORG');
                     }
                     break;
                 case 'X-ADDRESSBOOKSERVER-KIND':
-                    if ('GROUP' === strtoupper($property->getValue())) {
+                    if ('GROUP' === strtoupper((string) $property->getValue())) {
                         $newProperty = $output->createProperty('KIND', 'GROUP');
                     }
                     break;
@@ -274,10 +274,11 @@ protected function convertBinaryToUri(Component\VCard $output, Binary $newProper
             $newTypes = [];
             foreach ($parameters['TYPE']->getParts() as $typePart) {
                 if (in_array(
-                    strtoupper($typePart),
-                    ['JPEG', 'PNG', 'GIF']
+                    strtoupper((string) $typePart),
+                    ['JPEG', 'PNG', 'GIF'],
+                    true
                 )) {
-                    $mimeType = 'image/'.strtolower($typePart);
+                    $mimeType = 'image/'.strtolower((string) $typePart);
                 } else {
                     $newTypes[] = $typePart;
                 }
@@ -292,7 +293,7 @@ protected function convertBinaryToUri(Component\VCard $output, Binary $newProper
             }
         }
 
-        $newProperty->setValue('data:'.$mimeType.';base64,'.base64_encode($value));
+        $newProperty->setValue('data:'.$mimeType.';base64,'.base64_encode((string) $value));
 
         return $newProperty;
     }
@@ -313,7 +314,7 @@ protected function convertUriToBinary(Component\VCard $output, Uri $newProperty)
         $value = $newProperty->getValue();
 
         // Only converting data: uris
-        if ('data:' !== substr($value, 0, 5)) {
+        if (!str_starts_with((string) $value, 'data:')) {
             return $newProperty;
         }
 
@@ -325,12 +326,12 @@ protected function convertUriToBinary(Component\VCard $output, Uri $newProperty)
             'BINARY'
         );
 
-        $mimeType = substr($value, 5, strpos($value, ',') - 5);
+        $mimeType = substr((string) $value, 5, strpos((string) $value, ',') - 5);
         if (strpos($mimeType, ';')) {
             $mimeType = substr($mimeType, 0, strpos($mimeType, ';'));
-            $newProperty->setValue(base64_decode(substr($value, strpos($value, ',') + 1)));
+            $newProperty->setValue(base64_decode(substr((string) $value, strpos((string) $value, ',') + 1), true));
         } else {
-            $newProperty->setValue(substr($value, strpos($value, ',') + 1));
+            $newProperty->setValue(substr((string) $value, strpos((string) $value, ',') + 1));
         }
         unset($value);
 
@@ -367,7 +368,7 @@ protected function convertParameters40(Property $newProperty, array $parameters)
                 // that's now PREF=1.
                 case 'TYPE':
                     foreach ($param->getParts() as $paramPart) {
-                        if ('PREF' === strtoupper($paramPart)) {
+                        if ('PREF' === strtoupper((string) $paramPart)) {
                             $newProperty->add('PREF', '1');
                         } else {
                             $newProperty->add($param->name, $paramPart);
@@ -402,7 +403,7 @@ protected function convertParameters30(Property $newProperty, array $parameters)
                 case 'ENCODING':
                     // This value only existed in vCard 2.1, and should be
                     // removed for anything else.
-                    if ('QUOTED-PRINTABLE' !== strtoupper($param->getValue())) {
+                    if ('QUOTED-PRINTABLE' !== strtoupper((string) $param->getValue())) {
                         $newProperty->add($param->name, $param->getParts());
                     }
                     break;
@@ -413,7 +414,7 @@ protected function convertParameters30(Property $newProperty, array $parameters)
                      * Any other PREF numbers we'll drop.
                      */
                 case 'PREF':
-                    if ('1' == $param->getValue()) {
+                    if ('1' === (string) $param->getValue()) {
                         $newProperty->add('TYPE', 'PREF');
                     }
                     break;
diff --git a/rector.php b/rector.php
new file mode 100644
index 000000000..201fc8090
--- /dev/null
+++ b/rector.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+
+return RectorConfig::configure()
+    ->withPaths([
+        __DIR__.'/lib',
+        __DIR__.'/tests',
+    ])
+    // uncomment to reach your current PHP version
+    ->withPhpSets(false, true)
+    ->withTypeCoverageLevel(0)
+    ->withDeadCodeLevel(0)
+    ->withCodeQualityLevel(0);
diff --git a/tests/VObject/CliTest.php b/tests/VObject/CliTest.php
index c57d25226..5240bdd63 100644
--- a/tests/VObject/CliTest.php
+++ b/tests/VObject/CliTest.php
@@ -154,7 +154,7 @@ public function testConvertJson(): void
     public function testConvertJCardPretty(): void
     {
         if (version_compare(PHP_VERSION, '5.4.0') < 0) {
-            $this->markTestSkipped('This test required PHP 5.4.0');
+            self::markTestSkipped('This test required PHP 5.4.0');
         }
 
         $inputStream = fopen('php://memory', 'r+');
@@ -272,44 +272,60 @@ public function testConvertMimeDir(): void
         );
     }
 
-    public function testConvertDefaultFormats(): void
+    public static function provideFormats(): array
     {
-        $outputFile = $this->sabreTempDir.'bar.json';
-
-        self::assertEquals(
-            2,
-            $this->cli->main(['vobject', 'convert', 'foo.json', $outputFile])
-        );
-
-        self::assertEquals('json', $this->cli->inputFormat);
-        self::assertEquals('json', $this->cli->format);
+        return [
+            ['foo.json', 'bar.json', 'json'],
+            ['foo.ics', 'bar.ics', 'mimedir'],
+        ];
     }
 
-    public function testConvertDefaultFormats2(): void
+    /**
+     * @dataProvider provideFormats
+     */
+    public function testConvertDefaultFormats($inputFilename, $outputFilename, $format): void
     {
-        $outputFile = $this->sabreTempDir.'bar.ics';
+        $triggeredWarning = null;
 
-        self::assertEquals(
-            2,
-            $this->cli->main(['vobject', 'convert', 'foo.ics', $outputFile])
-        );
+        // Set an error handler to catch the native PHP Warning
+        set_error_handler(function (int $errno, string $errstr) use (&$triggeredWarning) {
+            $triggeredWarning = $errstr;
+
+            return true; // Prevents the error from propagating further
+        }, E_WARNING);
+
+        $outputFile = $this->sabreTempDir.$outputFilename;
 
-        self::assertEquals('mimedir', $this->cli->inputFormat);
-        self::assertEquals('mimedir', $this->cli->format);
+        try {
+            self::assertEquals(
+                2,
+                $this->cli->main(['vobject', 'convert', $inputFilename, $outputFile])
+            );
+        } finally {
+            restore_error_handler();
+        }
+
+        self::assertNotNull($triggeredWarning, 'A PHP warning was expected but never triggered.');
+        self::assertStringContainsString(
+            "fopen($inputFilename): Failed to open stream: No such file or directory",
+            $triggeredWarning
+        );
+        self::assertEquals($format, $this->cli->inputFormat);
+        self::assertEquals($format, $this->cli->format);
     }
 
     public function testVCard3040(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
-        fwrite($inputStream, <<<VCARD
-BEGIN:VCARD
-VERSION:3.0
-PRODID:-//Sabre//Sabre VObject 3.1.0//EN
-FN:Cowboy Henk
-END:VCARD
-
-VCARD
+        fwrite($inputStream, <<<VCARD_WRAP
+        BEGIN:VCARD
+        VERSION:3.0
+        PRODID:-//Sabre//Sabre VObject 3.1.0//EN
+        FN:Cowboy Henk
+        END:VCARD
+        
+        VCARD_WRAP
         );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
@@ -341,14 +357,14 @@ public function testVCard4030(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
-        fwrite($inputStream, <<<VCARD
-BEGIN:VCARD
-VERSION:4.0
-PRODID:-//Sabre//Sabre VObject 3.1.0//EN
-FN:Cowboy Henk
-END:VCARD
-
-VCARD
+        fwrite($inputStream, <<<VCARD_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        PRODID:-//Sabre//Sabre VObject 3.1.0//EN
+        FN:Cowboy Henk
+        END:VCARD
+        
+        VCARD_WRAP
         );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
@@ -380,14 +396,14 @@ public function testVCard4021(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
-        fwrite($inputStream, <<<VCARD
-BEGIN:VCARD
-VERSION:4.0
-PRODID:-//Sabre//Sabre VObject 3.1.0//EN
-FN:Cowboy Henk
-END:VCARD
-
-VCARD
+        fwrite($inputStream, <<<VCARD_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        PRODID:-//Sabre//Sabre VObject 3.1.0//EN
+        FN:Cowboy Henk
+        END:VCARD
+        
+        VCARD_WRAP
         );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
@@ -402,15 +418,15 @@ public function testValidate(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
-        fwrite($inputStream, <<<VCARD
-BEGIN:VCARD
-VERSION:4.0
-PRODID:-//Sabre//Sabre VObject 3.1.0//EN
-UID:foo
-FN:Cowboy Henk
-END:VCARD
-
-VCARD
+        fwrite($inputStream, <<<VCARD_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        PRODID:-//Sabre//Sabre VObject 3.1.0//EN
+        UID:foo
+        FN:Cowboy Henk
+        END:VCARD
+        
+        VCARD_WRAP
         );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
@@ -426,12 +442,12 @@ public function testValidateFail(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
-        fwrite($inputStream, <<<VCARD
-BEGIN:VCALENDAR
-VERSION:2.0
-END:VCARD
-
-VCARD
+        fwrite($inputStream, <<<VCARD_WRAP
+        BEGIN:VCALENDAR
+        VERSION:2.0
+        END:VCARD
+        
+        VCARD_WRAP
         );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
@@ -466,12 +482,12 @@ public function testRepair(): void
     {
         $inputStream = fopen('php://memory', 'r+');
 
-        fwrite($inputStream, <<<VCARD
-BEGIN:VCARD
-VERSION:5.0
-END:VCARD
-
-VCARD
+        fwrite($inputStream, <<<VCARD_WRAP
+        BEGIN:VCARD
+        VERSION:5.0
+        END:VCARD
+        
+        VCARD_WRAP
         );
         rewind($inputStream);
         $this->cli->stdin = $inputStream;
diff --git a/tests/VObject/Component/AvailableTest.php b/tests/VObject/Component/AvailableTest.php
index 98202ffcb..68c9d90f0 100644
--- a/tests/VObject/Component/AvailableTest.php
+++ b/tests/VObject/Component/AvailableTest.php
@@ -13,26 +13,26 @@ class AvailableTest extends TestCase
 {
     public function testAvailableComponent(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:AVAILABLE
-END:AVAILABLE
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:AVAILABLE
+        END:AVAILABLE
+        END:VCALENDAR
+        VCAL_WRAP;
         $document = Reader::read($vcal);
         self::assertInstanceOf(Available::class, $document->AVAILABLE);
     }
 
     public function testGetEffectiveStartEnd(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:AVAILABLE
-DTSTART:20150717T162200Z
-DTEND:20150717T172200Z
-END:AVAILABLE
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:AVAILABLE
+        DTSTART:20150717T162200Z
+        DTEND:20150717T172200Z
+        END:AVAILABLE
+        END:VCALENDAR
+        VCAL_WRAP;
 
         $document = Reader::read($vcal);
         $tz = new \DateTimeZone('UTC');
@@ -47,14 +47,14 @@ public function testGetEffectiveStartEnd(): void
 
     public function testGetEffectiveStartEndDuration(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:AVAILABLE
-DTSTART:20150717T162200Z
-DURATION:PT1H
-END:AVAILABLE
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:AVAILABLE
+        DTSTART:20150717T162200Z
+        DURATION:PT1H
+        END:AVAILABLE
+        END:VCALENDAR
+        VCAL_WRAP;
 
         $document = Reader::read($vcal);
         $tz = new \DateTimeZone('UTC');
diff --git a/tests/VObject/Component/VAlarmTest.php b/tests/VObject/Component/VAlarmTest.php
index a67991ff4..33da9410c 100644
--- a/tests/VObject/Component/VAlarmTest.php
+++ b/tests/VObject/Component/VAlarmTest.php
@@ -16,7 +16,7 @@ public function testInTimeRange(VAlarm $valarm, \DateTime $start, \DateTime $end
         self::assertEquals($outcome, $valarm->isInTimeRange($start, $end));
     }
 
-    public function timeRangeTestData(): array
+    public static function timeRangeTestData(): array
     {
         $tests = [];
 
diff --git a/tests/VObject/Component/VAvailabilityTest.php b/tests/VObject/Component/VAvailabilityTest.php
index 67499e98e..d8040f851 100644
--- a/tests/VObject/Component/VAvailabilityTest.php
+++ b/tests/VObject/Component/VAvailabilityTest.php
@@ -14,12 +14,12 @@ class VAvailabilityTest extends TestCase
 {
     public function testVAvailabilityComponent(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:VAVAILABILITY
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:VAVAILABILITY
+        END:VAVAILABILITY
+        END:VCALENDAR
+        VCAL_WRAP;
         $document = Reader::read($vcal);
 
         self::assertInstanceOf(VAvailability::class, $document->VAVAILABILITY);
@@ -27,14 +27,14 @@ public function testVAvailabilityComponent(): void
 
     public function testGetEffectiveStartEnd(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:VAVAILABILITY
-DTSTART:20150717T162200Z
-DTEND:20150717T172200Z
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:VAVAILABILITY
+        DTSTART:20150717T162200Z
+        DTEND:20150717T172200Z
+        END:VAVAILABILITY
+        END:VCALENDAR
+        VCAL_WRAP;
 
         $document = Reader::read($vcal);
         $tz = new \DateTimeZone('UTC');
@@ -49,14 +49,14 @@ public function testGetEffectiveStartEnd(): void
 
     public function testGetEffectiveStartDuration(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:VAVAILABILITY
-DTSTART:20150717T162200Z
-DURATION:PT1H
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:VAVAILABILITY
+        DTSTART:20150717T162200Z
+        DURATION:PT1H
+        END:VAVAILABILITY
+        END:VCALENDAR
+        VCAL_WRAP;
 
         $document = Reader::read($vcal);
         $tz = new \DateTimeZone('UTC');
@@ -71,12 +71,12 @@ public function testGetEffectiveStartDuration(): void
 
     public function testGetEffectiveStartEndUnbound(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:VAVAILABILITY
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:VAVAILABILITY
+        END:VAVAILABILITY
+        END:VCALENDAR
+        VCAL_WRAP;
 
         $document = Reader::read($vcal);
         self::assertEquals(
@@ -90,12 +90,12 @@ public function testGetEffectiveStartEndUnbound(): void
 
     public function testIsInTimeRangeUnbound(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:VAVAILABILITY
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:VAVAILABILITY
+        END:VAVAILABILITY
+        END:VCALENDAR
+        VCAL_WRAP;
 
         $document = Reader::read($vcal);
         self::assertTrue(
@@ -105,14 +105,14 @@ public function testIsInTimeRangeUnbound(): void
 
     public function testIsInTimeRangeOutside(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:VAVAILABILITY
-DTSTART:20140101T000000Z
-DTEND:20140102T000000Z
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:VAVAILABILITY
+        DTSTART:20140101T000000Z
+        DTEND:20140102T000000Z
+        END:VAVAILABILITY
+        END:VCALENDAR
+        VCAL_WRAP;
 
         $document = Reader::read($vcal);
         self::assertFalse(
@@ -124,54 +124,54 @@ public function testRFCxxxSection3Part1AvailabilityPropRequired(): void
     {
         // UID and DTSTAMP are present.
         self::assertIsValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
 
         // UID and DTSTAMP are missing.
         self::assertIsNotValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
 
         // DTSTAMP is missing.
         self::assertIsNotValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
 
         // UID is missing.
         self::assertIsNotValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-DTSTAMP:20111005T133225Z
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            DTSTAMP:20111005T133225Z
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
     }
 
@@ -224,14 +224,14 @@ public function testRFCxxxSection3Part1AvailabilityPropDtendDuration(): void
 
     public function testAvailableSubComponent(): void
     {
-        $vcal = <<<VCAL
-BEGIN:VCALENDAR
-BEGIN:VAVAILABILITY
-BEGIN:AVAILABLE
-END:AVAILABLE
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL;
+        $vcal = <<<VCAL_WRAP
+        BEGIN:VCALENDAR
+        BEGIN:VAVAILABILITY
+        BEGIN:AVAILABLE
+        END:AVAILABLE
+        END:VAVAILABILITY
+        END:VCALENDAR
+        VCAL_WRAP;
         $document = Reader::read($vcal);
 
         self::assertInstanceOf(Available::class, $document->VAVAILABILITY->AVAILABLE);
@@ -241,91 +241,91 @@ public function testRFCxxxSection3Part1AvailablePropRequired(): void
     {
         // UID, DTSTAMP and DTSTART are present.
         self::assertIsValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-BEGIN:AVAILABLE
-UID:foo@test
-DTSTAMP:20111005T133225Z
-DTSTART:20111005T133225Z
-END:AVAILABLE
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            BEGIN:AVAILABLE
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            DTSTART:20111005T133225Z
+            END:AVAILABLE
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
 
         // UID, DTSTAMP and DTSTART are missing.
         self::assertIsNotValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-BEGIN:AVAILABLE
-END:AVAILABLE
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            BEGIN:AVAILABLE
+            END:AVAILABLE
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
 
         // UID is missing.
         self::assertIsNotValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-BEGIN:AVAILABLE
-DTSTAMP:20111005T133225Z
-DTSTART:20111005T133225Z
-END:AVAILABLE
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            BEGIN:AVAILABLE
+            DTSTAMP:20111005T133225Z
+            DTSTART:20111005T133225Z
+            END:AVAILABLE
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
 
         // DTSTAMP is missing.
         self::assertIsNotValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-BEGIN:AVAILABLE
-UID:foo@test
-DTSTART:20111005T133225Z
-END:AVAILABLE
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            BEGIN:AVAILABLE
+            UID:foo@test
+            DTSTART:20111005T133225Z
+            END:AVAILABLE
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
 
         // DTSTART is missing.
         self::assertIsNotValid(Reader::read(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-BEGIN:AVAILABLE
-UID:foo@test
-DTSTAMP:20111005T133225Z
-END:AVAILABLE
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            BEGIN:AVAILABLE
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            END:AVAILABLE
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP
         ));
     }
 
@@ -411,8 +411,8 @@ protected function assertIsValid(VObject\Document $document): void
     {
         $validationResult = $document->validate();
         if ($validationResult) {
-            $messages = array_map(function ($item) { return $item['message']; }, $validationResult);
-            $this->fail('Failed to assert that the supplied document is a valid document. Validation messages: '.implode(', ', $messages));
+            $messages = array_map(fn ($item) => $item['message'], $validationResult);
+            self::fail('Failed to assert that the supplied document is a valid document. Validation messages: '.implode(', ', $messages));
         }
         self::assertEmpty($document->validate());
     }
@@ -425,17 +425,17 @@ protected function assertIsNotValid(VObject\Document $document): void
     protected function template(array $properties)
     {
         return $this->_template(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-…
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL,
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            …
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP,
             $properties
         );
     }
@@ -443,22 +443,22 @@ protected function template(array $properties)
     protected function templateAvailable(array $properties)
     {
         return $this->_template(
-            <<<VCAL
-BEGIN:VCALENDAR
-VERSION:2.0
-PRODID:-//id
-BEGIN:VAVAILABILITY
-UID:foo@test
-DTSTAMP:20111005T133225Z
-BEGIN:AVAILABLE
-UID:foo@test
-DTSTAMP:20111005T133225Z
-DTSTART:20111005T133225Z
-…
-END:AVAILABLE
-END:VAVAILABILITY
-END:VCALENDAR
-VCAL,
+            <<<VCAL_WRAP
+            BEGIN:VCALENDAR
+            VERSION:2.0
+            PRODID:-//id
+            BEGIN:VAVAILABILITY
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            BEGIN:AVAILABLE
+            UID:foo@test
+            DTSTAMP:20111005T133225Z
+            DTSTART:20111005T133225Z
+            …
+            END:AVAILABLE
+            END:VAVAILABILITY
+            END:VCALENDAR
+            VCAL_WRAP,
             $properties
         );
     }
diff --git a/tests/VObject/Component/VCalendarTest.php b/tests/VObject/Component/VCalendarTest.php
index 847e17d02..ea1fe61b4 100644
--- a/tests/VObject/Component/VCalendarTest.php
+++ b/tests/VObject/Component/VCalendarTest.php
@@ -31,7 +31,7 @@ public function testExpand(string $input, string $output, string $timeZone = 'UT
         self::assertVObjectEqualsVObject($output, $vcal->serialize());
     }
 
-    public function expandData(): array
+    public static function expandData(): array
     {
         $tests = [];
 
diff --git a/tests/VObject/Component/VCardTest.php b/tests/VObject/Component/VCardTest.php
index ff4979ed4..1ae83b81e 100644
--- a/tests/VObject/Component/VCardTest.php
+++ b/tests/VObject/Component/VCardTest.php
@@ -31,7 +31,7 @@ public function testValidate(string $input, array $expectedWarnings, string $exp
         );
     }
 
-    public function validateData(): array
+    public static function validateData(): array
     {
         $tests = [];
 
diff --git a/tests/VObject/Component/VEventTest.php b/tests/VObject/Component/VEventTest.php
index 5944ea574..9c79c245d 100644
--- a/tests/VObject/Component/VEventTest.php
+++ b/tests/VObject/Component/VEventTest.php
@@ -14,7 +14,7 @@ public function testInTimeRange(VEvent $vevent, \DateTime $start, \DateTime $end
         self::assertEquals($outcome, $vevent->isInTimeRange($start, $end));
     }
 
-    public function timeRangeTestData(): array
+    public static function timeRangeTestData(): array
     {
         $tests = [];
 
diff --git a/tests/VObject/Component/VJournalTest.php b/tests/VObject/Component/VJournalTest.php
index 98f478896..d0419253d 100644
--- a/tests/VObject/Component/VJournalTest.php
+++ b/tests/VObject/Component/VJournalTest.php
@@ -68,7 +68,7 @@ public function testValidateBroken(): void
         );
     }
 
-    public function timeRangeTestData(): array
+    public static function timeRangeTestData(): array
     {
         $calendar = new VCalendar();
 
diff --git a/tests/VObject/Component/VTodoTest.php b/tests/VObject/Component/VTodoTest.php
index 899d93982..5bd28c6fe 100644
--- a/tests/VObject/Component/VTodoTest.php
+++ b/tests/VObject/Component/VTodoTest.php
@@ -15,7 +15,7 @@ public function testInTimeRange(VTodo $vtodo, \DateTime $start, \DateTime $end,
         self::assertEquals($outcome, $vtodo->isInTimeRange($start, $end));
     }
 
-    public function timeRangeTestData(): array
+    public static function timeRangeTestData(): array
     {
         $tests = [];
 
diff --git a/tests/VObject/ComponentTest.php b/tests/VObject/ComponentTest.php
index c48480983..8e930a564 100644
--- a/tests/VObject/ComponentTest.php
+++ b/tests/VObject/ComponentTest.php
@@ -546,7 +546,7 @@ public function testValidateRepairShouldDeduplicatePropertiesWhenValuesAreEqual(
         self::assertCount(1, $component->GIR);
     }
 
-    public function ruleData(): array
+    public static function ruleData(): array
     {
         return [
             [[], 2],
diff --git a/tests/VObject/DateTimeParserTest.php b/tests/VObject/DateTimeParserTest.php
index cdf0fe990..2ae7a6897 100644
--- a/tests/VObject/DateTimeParserTest.php
+++ b/tests/VObject/DateTimeParserTest.php
@@ -189,7 +189,7 @@ public function testBadVCardTime(): void
         DateTimeParser::parseVCardTime('23:12:166');
     }
 
-    public function vcardDates(): array
+    public static function vcardDates(): array
     {
         return [
             [
diff --git a/tests/VObject/ITip/BrokerTester.php b/tests/VObject/ITip/BrokerTester.php
index cc01ed3f9..43eb91814 100644
--- a/tests/VObject/ITip/BrokerTester.php
+++ b/tests/VObject/ITip/BrokerTester.php
@@ -40,6 +40,7 @@ public function parse($oldMessage, $newMessage, array $expected = [], string $cu
                         $message->message->serialize()
                     );
                 } else {
+                    // @phpstan-ignore property.dynamicName
                     self::assertEquals($val, $message->$key);
                 }
             }
@@ -59,8 +60,9 @@ public function process($input, $existingObject = null, $expected = false): void
         $vcal = Reader::read($input);
 
         $mainComponent = new VEvent($vcal, 'VEVENT');
-        foreach ($vcal->getComponents() as $mainComponent) {
-            if ('VEVENT' === $mainComponent->name) {
+        foreach ($vcal->getComponents() as $nextComponent) {
+            if ('VEVENT' === $nextComponent->name) {
+                $mainComponent = $nextComponent;
                 break;
             }
         }
@@ -76,7 +78,7 @@ public function process($input, $existingObject = null, $expected = false): void
             $message->sender = $mainComponent->ATTENDEE->getValue();
             $message->senderName = isset($mainComponent->ATTENDEE['CN']) ? $mainComponent->ATTENDEE['CN']->getValue() : null;
             $message->recipient = $mainComponent->ORGANIZER->getValue();
-            $message->recipientName = isset($mainComponent->ORGANIZER['CN']) ? $mainComponent->ORGANIZER['CN'] : null;
+            $message->recipientName = $mainComponent->ORGANIZER['CN'] ?? null;
         }
 
         $broker = new Broker();
diff --git a/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php b/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php
index e3f18f15e..c0afe4578 100644
--- a/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php
+++ b/tests/VObject/ITip/BrokerTimezoneInParseEventInfoWithoutMasterTest.php
@@ -70,7 +70,6 @@ public function testTimezoneInParseEventInfoWithoutMaster(): void
         $broker = new Broker();
 
         $reflectionMethod = new \ReflectionMethod($broker, 'parseEventInfo');
-        $reflectionMethod->setAccessible(true);
         $data = $reflectionMethod->invoke($broker, $calendar);
         self::assertInstanceOf('DateTimeZone', $data['timezone']);
         self::assertEquals('Europe/Minsk', $data['timezone']->getName());
diff --git a/tests/VObject/Parser/MimeDirTest.php b/tests/VObject/Parser/MimeDirTest.php
index 2fb436d0f..a265b4216 100644
--- a/tests/VObject/Parser/MimeDirTest.php
+++ b/tests/VObject/Parser/MimeDirTest.php
@@ -101,7 +101,7 @@ public function testDecodeUnsupportedInlineCharset(): void
         $mimeDir->parse($vcard);
     }
 
-    public function provideEmptyParserInput(): array
+    public static function provideEmptyParserInput(): array
     {
         return [
             [null, 'No input provided to parse'],
@@ -212,7 +212,7 @@ public function testBrokenMultilineContentDoesBreakImport($vcalendar): void
         $mimeDir->parse($vcalendar);
     }
 
-    public function provideBrokenVCalendar(): array
+    public static function provideBrokenVCalendar(): array
     {
         return [[<<<EOF
 BEGIN:VCALENDAR
@@ -274,6 +274,7 @@ public function testPropertyName0(): void
 
         $mimeDir = new MimeDir();
         $vevent = $mimeDir->parse($iCal);
+        // @phpstan-ignore property.dynamicName
         self::assertEquals('test', $vevent->VEVENT->{0}->getValue());
     }
 
diff --git a/tests/VObject/Parser/XmlTest.php b/tests/VObject/Parser/XmlTest.php
index 6491d087b..1ad36474d 100644
--- a/tests/VObject/Parser/XmlTest.php
+++ b/tests/VObject/Parser/XmlTest.php
@@ -2704,6 +2704,6 @@ protected function assertXMLReflexivelyEqualsToMimeDir(string $xml, string $mime
         self::assertXMLEqualsToMimeDir($xml, $mimedir);
 
         $component = VObject\Reader::read($mimedir);
-        self::assertXmlStringEqualsXmlString($xml, VObject\Writer::writeXML($component));
+        self::assertXmlStringEqualsXmlString($xml, VObject\Writer::writeXml($component));
     }
 }
diff --git a/tests/VObject/Property/ICalendar/CalAddressTest.php b/tests/VObject/Property/ICalendar/CalAddressTest.php
index b774f4fbc..1142f2a9d 100644
--- a/tests/VObject/Property/ICalendar/CalAddressTest.php
+++ b/tests/VObject/Property/ICalendar/CalAddressTest.php
@@ -20,7 +20,7 @@ public function testGetNormalizedValue(string $expected, string $input): void
         );
     }
 
-    public function values(): array
+    public static function values(): array
     {
         return [
             ['mailto:a@b.com', 'mailto:a@b.com'],
diff --git a/tests/VObject/Property/ICalendar/DateTimeTest.php b/tests/VObject/Property/ICalendar/DateTimeTest.php
index 5a70b2641..f0728d3ed 100644
--- a/tests/VObject/Property/ICalendar/DateTimeTest.php
+++ b/tests/VObject/Property/ICalendar/DateTimeTest.php
@@ -102,7 +102,7 @@ public function testSetDateTimeDATE(): void
 
         self::assertEquals('19850704', (string) $elem);
         self::assertNull($elem['TZID']);
-        self::assertEquals('DATE', (string) $elem['VALUE']);
+        self::assertEquals('DATE', $elem['VALUE']);
 
         self::assertFalse($elem->hasTime());
     }
diff --git a/tests/VObject/Property/TextTest.php b/tests/VObject/Property/TextTest.php
index 0fa320bfe..aadbd4141 100644
--- a/tests/VObject/Property/TextTest.php
+++ b/tests/VObject/Property/TextTest.php
@@ -66,14 +66,14 @@ public function testSerializeQuotedPrintableFold(): void
 
     public function testValidateMinimumPropValue(): void
     {
-        $vcard = <<<IN
-BEGIN:VCARD
-VERSION:4.0
-UID:foo
-FN:Hi!
-N:A
-END:VCARD
-IN;
+        $vcard = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        UID:foo
+        FN:Hi!
+        N:A
+        END:VCARD
+        IN_WRAP;
 
         $vcard = \Sabre\VObject\Reader::read($vcard);
         self::assertCount(1, $vcard->validate());
diff --git a/tests/VObject/Property/VCard/DateAndOrTimeTest.php b/tests/VObject/Property/VCard/DateAndOrTimeTest.php
index 8e2cb3207..5d24850fc 100644
--- a/tests/VObject/Property/VCard/DateAndOrTimeTest.php
+++ b/tests/VObject/Property/VCard/DateAndOrTimeTest.php
@@ -19,7 +19,7 @@ public function testGetJsonValue(string $input, string $output): void
         self::assertEquals([$output], $prop->getJsonValue());
     }
 
-    public function dates(): array
+    public static function dates(): array
     {
         return [
             [
diff --git a/tests/VObject/ReaderTest.php b/tests/VObject/ReaderTest.php
index 645ed1813..7b6c953fd 100644
--- a/tests/VObject/ReaderTest.php
+++ b/tests/VObject/ReaderTest.php
@@ -318,7 +318,7 @@ public function testReadForgiving(): void
         $caught = false;
         try {
             Reader::read(implode("\r\n", $data));
-        } catch (ParseException $e) {
+        } catch (ParseException) {
             $caught = true;
         }
 
@@ -348,7 +348,7 @@ public function testReadWithInvalidLine(): void
         $caught = false;
         try {
             Reader::read(implode("\r\n", $data));
-        } catch (ParseException $e) {
+        } catch (ParseException) {
             $caught = true;
         }
 
diff --git a/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php b/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php
index 4f434dd2a..aca783d3c 100644
--- a/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php
+++ b/tests/VObject/Recur/EventIterator/HandleRDateExpandTest.php
@@ -51,7 +51,7 @@ public function testExpand(): void
             new \DateTimeImmutable('2015-10-20', $utc),
         ];
 
-        $result = array_map(function ($ev) {return $ev->DTSTART->getDateTime(); }, $result);
+        $result = array_map(fn ($ev) => $ev->DTSTART->getDateTime(), $result);
         self::assertEquals($expected, $result);
     }
 }
diff --git a/tests/VObject/Recur/EventIterator/MainTest.php b/tests/VObject/Recur/EventIterator/MainTest.php
index bce4bcd92..1899feea3 100644
--- a/tests/VObject/Recur/EventIterator/MainTest.php
+++ b/tests/VObject/Recur/EventIterator/MainTest.php
@@ -33,7 +33,7 @@ public function testValues(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         self::assertTrue($it->isInfinite());
     }
@@ -58,7 +58,7 @@ public function testInvalidFreq(): void
         $ev->add($dtStart);
         $vcal->add($ev);
 
-        new EventIterator($vcal, (string) $ev->UID);
+        new EventIterator($vcal, $ev->UID);
     }
 
     /**
@@ -252,7 +252,7 @@ public function testDailyByDayByHour(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // Grabbing the next 12 items
         $max = 12;
@@ -304,7 +304,7 @@ public function testDailyByHour(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // Grabbing the next 12 items
         $max = 12;
@@ -356,7 +356,7 @@ public function testDailyByDay(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // Grabbing the next 12 items
         $max = 12;
@@ -408,7 +408,7 @@ public function testWeekly(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // Max is to prevent overflow
         $max = 12;
@@ -458,7 +458,7 @@ public function testWeeklyByDayByHour(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // Grabbing the next 12 items
         $max = 15;
@@ -513,7 +513,7 @@ public function testWeeklyByDaySpecificHour(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // Grabbing the next 12 items
         $max = 12;
@@ -565,7 +565,7 @@ public function testWeeklyByDay(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // Grabbing the next 12 items
         $max = 12;
@@ -617,7 +617,7 @@ public function testMonthly(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 14;
         $result = [];
@@ -661,7 +661,7 @@ public function testMonthlyEndOfMonth(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 14;
         $result = [];
@@ -719,7 +719,7 @@ public function testMonthlyByMonthDay(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 14;
         $result = [];
@@ -772,7 +772,7 @@ public function testMonthlyByDay(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
@@ -827,7 +827,7 @@ public function testMonthlyByDayByMonthDay(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
@@ -876,7 +876,7 @@ public function testMonthlyByDayBySetPos(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
@@ -930,7 +930,7 @@ public function testYearly(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
@@ -979,7 +979,7 @@ public function testYearlyLeapYear(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
@@ -1021,7 +1021,7 @@ public function testYearlyByMonth(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
@@ -1068,7 +1068,7 @@ public function testYearlyByMonthByDay(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
@@ -1115,7 +1115,7 @@ public function testFastForward(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         // The idea is that we're fast-forwarding too far in the future, so
         // there will be no results left.
@@ -1157,7 +1157,7 @@ public function testFastForwardAllDayEventThatStopAtTheStartTime(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $it->fastForward(new \DateTimeImmutable('2011-04-05T000000', new \DateTimeZone('UTC')));
 
@@ -1199,7 +1199,7 @@ public function testComplexExclusions(): void
 
         $vcal->add($ev);
 
-        $it = new EventIterator($vcal, (string) $ev->UID);
+        $it = new EventIterator($vcal, $ev->UID);
 
         $max = 20;
         $result = [];
diff --git a/tests/VObject/Recur/RRuleIteratorTest.php b/tests/VObject/Recur/RRuleIteratorTest.php
index ea049a170..639949209 100644
--- a/tests/VObject/Recur/RRuleIteratorTest.php
+++ b/tests/VObject/Recur/RRuleIteratorTest.php
@@ -43,11 +43,11 @@ public function test2HourlyOnDstTransition(string $start, array $expected): void
         );
     }
 
-    public function dst2HourlyTransitionProvider(): iterable
+    public static function dst2HourlyTransitionProvider(): iterable
     {
         yield 'On transition start' => [
-            'Start' => '2023-03-26 00:00:00',
-            'Expected' => [
+            'start' => '2023-03-26 00:00:00',
+            'expected' => [
                 '2023-03-26 00:00:00',
                 '2023-03-26 03:00:00',
                 '2023-03-26 04:00:00',
@@ -56,8 +56,8 @@ public function dst2HourlyTransitionProvider(): iterable
             ],
         ];
         yield 'During transition' => [
-            'Start' => '2023-03-26 00:15:00',
-            'Expected' => [
+            'start' => '2023-03-26 00:15:00',
+            'expected' => [
                 '2023-03-26 00:15:00',
                 '2023-03-26 03:15:00',
                 '2023-03-26 04:15:00',
@@ -66,8 +66,8 @@ public function dst2HourlyTransitionProvider(): iterable
             ],
         ];
         yield 'On transition end' => [
-            'Start' => '2023-03-26 01:00:00',
-            'Expected' => [
+            'start' => '2023-03-26 01:00:00',
+            'expected' => [
                 '2023-03-26 01:00:00',
                 '2023-03-26 03:00:00',
                 '2023-03-26 05:00:00',
@@ -76,8 +76,8 @@ public function dst2HourlyTransitionProvider(): iterable
             ],
         ];
         yield 'After transition end' => [
-            'Start' => '2023-03-26 01:15:00',
-            'Expected' => [
+            'start' => '2023-03-26 01:15:00',
+            'expected' => [
                 '2023-03-26 01:15:00',
                 '2023-03-26 03:15:00',
                 '2023-03-26 05:15:00',
@@ -101,11 +101,11 @@ public function testHourlyOnDstTransition(string $start, array $expected): void
         );
     }
 
-    public function dst6HourlyTransitionProvider(): iterable
+    public static function dst6HourlyTransitionProvider(): iterable
     {
         yield 'On transition start' => [
-            'Start' => '2023-03-25 20:00:00',
-            'Expected' => [
+            'start' => '2023-03-25 20:00:00',
+            'expected' => [
                 '2023-03-25 20:00:00',
                 '2023-03-26 03:00:00',
                 '2023-03-26 08:00:00',
@@ -114,8 +114,8 @@ public function dst6HourlyTransitionProvider(): iterable
             ],
         ];
         yield 'During transition' => [
-            'Start' => '2023-03-25 20:15:00',
-            'Expected' => [
+            'start' => '2023-03-25 20:15:00',
+            'expected' => [
                 '2023-03-25 20:15:00',
                 '2023-03-26 03:15:00',
                 '2023-03-26 08:15:00',
@@ -124,8 +124,8 @@ public function dst6HourlyTransitionProvider(): iterable
             ],
         ];
         yield 'On transition end' => [
-            'Start' => '2023-03-25 21:00:00',
-            'Expected' => [
+            'start' => '2023-03-25 21:00:00',
+            'expected' => [
                 '2023-03-25 21:00:00',
                 '2023-03-26 03:00:00',
                 '2023-03-26 09:00:00',
@@ -134,8 +134,8 @@ public function dst6HourlyTransitionProvider(): iterable
             ],
         ];
         yield 'After transition end' => [
-            'Start' => '2023-03-25 21:15:00',
-            'Expected' => [
+            'start' => '2023-03-25 21:15:00',
+            'expected' => [
                 '2023-03-25 21:15:00',
                 '2023-03-26 03:15:00',
                 '2023-03-26 09:15:00',
@@ -292,11 +292,11 @@ public function testDailyOnDstTransition(string $start, array $expected): void
         );
     }
 
-    public function dstDailyTransitionProvider(): iterable
+    public static function dstDailyTransitionProvider(): iterable
     {
         yield 'On transition start' => [
-            'Start' => '2023-03-24 02:00:00',
-            'Expected' => [
+            'start' => '2023-03-24 02:00:00',
+            'expected' => [
                 '2023-03-24 02:00:00',
                 '2023-03-25 02:00:00',
                 '2023-03-26 03:00:00',
@@ -305,8 +305,8 @@ public function dstDailyTransitionProvider(): iterable
             ],
         ];
         yield 'During transition' => [
-            'Start' => '2023-03-24 02:15:00',
-            'Expected' => [
+            'start' => '2023-03-24 02:15:00',
+            'expected' => [
                 '2023-03-24 02:15:00',
                 '2023-03-25 02:15:00',
                 '2023-03-26 03:15:00',
@@ -315,8 +315,8 @@ public function dstDailyTransitionProvider(): iterable
             ],
         ];
         yield 'On transition end' => [
-            'Start' => '2023-03-24 03:00:00',
-            'Expected' => [
+            'start' => '2023-03-24 03:00:00',
+            'expected' => [
                 '2023-03-24 03:00:00',
                 '2023-03-25 03:00:00',
                 '2023-03-26 03:00:00',
@@ -325,8 +325,8 @@ public function dstDailyTransitionProvider(): iterable
             ],
         ];
         yield 'After transition end' => [
-            'Start' => '2023-03-24 03:15:00',
-            'Expected' => [
+            'start' => '2023-03-24 03:15:00',
+            'expected' => [
                 '2023-03-24 03:15:00',
                 '2023-03-25 03:15:00',
                 '2023-03-26 03:15:00',
@@ -499,11 +499,11 @@ public function testWeeklyOnDstTransition(string $start, array $expected): void
         );
     }
 
-    public function dstWeeklyTransitionProvider(): iterable
+    public static function dstWeeklyTransitionProvider(): iterable
     {
         yield 'On transition start' => [
-            'Start' => '2023-03-12 02:00:00',
-            'Expected' => [
+            'start' => '2023-03-12 02:00:00',
+            'expected' => [
                 '2023-03-12 02:00:00',
                 '2023-03-19 02:00:00',
                 '2023-03-26 03:00:00',
@@ -512,8 +512,8 @@ public function dstWeeklyTransitionProvider(): iterable
             ],
         ];
         yield 'During transition' => [
-            'Start' => '2023-03-12 02:15:00',
-            'Expected' => [
+            'start' => '2023-03-12 02:15:00',
+            'expected' => [
                 '2023-03-12 02:15:00',
                 '2023-03-19 02:15:00',
                 '2023-03-26 03:15:00',
@@ -522,8 +522,8 @@ public function dstWeeklyTransitionProvider(): iterable
             ],
         ];
         yield 'On transition end' => [
-            'Start' => '2023-03-12 03:00:00',
-            'Expected' => [
+            'start' => '2023-03-12 03:00:00',
+            'expected' => [
                 '2023-03-12 03:00:00',
                 '2023-03-19 03:00:00',
                 '2023-03-26 03:00:00',
@@ -532,8 +532,8 @@ public function dstWeeklyTransitionProvider(): iterable
             ],
         ];
         yield 'After transition end' => [
-            'Start' => '2023-03-12 03:15:00',
-            'Expected' => [
+            'start' => '2023-03-12 03:15:00',
+            'expected' => [
                 '2023-03-12 03:15:00',
                 '2023-03-19 03:15:00',
                 '2023-03-26 03:15:00',
@@ -751,11 +751,11 @@ public function testMonthlyOnDstTransition(string $start, array $expected): void
         );
     }
 
-    public function dstMonthlyTransitionProvider(): iterable
+    public static function dstMonthlyTransitionProvider(): iterable
     {
         yield 'On transition start' => [
-            'Start' => '2023-01-26 02:00:00',
-            'Expected' => [
+            'start' => '2023-01-26 02:00:00',
+            'expected' => [
                 '2023-01-26 02:00:00',
                 '2023-02-26 02:00:00',
                 '2023-03-26 03:00:00',
@@ -764,8 +764,8 @@ public function dstMonthlyTransitionProvider(): iterable
             ],
         ];
         yield 'During transition' => [
-            'Start' => '2023-01-26 02:15:00',
-            'Expected' => [
+            'start' => '2023-01-26 02:15:00',
+            'expected' => [
                 '2023-01-26 02:15:00',
                 '2023-02-26 02:15:00',
                 '2023-03-26 03:15:00',
@@ -774,8 +774,8 @@ public function dstMonthlyTransitionProvider(): iterable
             ],
         ];
         yield 'On transition end' => [
-            'Start' => '2023-01-26 03:00:00',
-            'Expected' => [
+            'start' => '2023-01-26 03:00:00',
+            'expected' => [
                 '2023-01-26 03:00:00',
                 '2023-02-26 03:00:00',
                 '2023-03-26 03:00:00',
@@ -784,8 +784,8 @@ public function dstMonthlyTransitionProvider(): iterable
             ],
         ];
         yield 'After transition end' => [
-            'Start' => '2023-01-26 03:15:00',
-            'Expected' => [
+            'start' => '2023-01-26 03:15:00',
+            'expected' => [
                 '2023-01-26 03:15:00',
                 '2023-02-26 03:15:00',
                 '2023-03-26 03:15:00',
@@ -794,8 +794,8 @@ public function dstMonthlyTransitionProvider(): iterable
             ],
         ];
         yield 'During transition on 31st day of month' => [
-            'Start' => '2024-01-31 02:15:00',
-            'Expected' => [
+            'start' => '2024-01-31 02:15:00',
+            'expected' => [
                 '2024-01-31 02:15:00',
                 '2024-03-31 03:15:00',
                 '2024-05-31 02:15:00',
@@ -1160,11 +1160,11 @@ public function testYearlyOnDstTransition(string $start, array $expected): void
         );
     }
 
-    public function dstYearlyTransitionProvider(): iterable
+    public static function dstYearlyTransitionProvider(): iterable
     {
         yield 'On transition start' => [
-            'Start' => '2021-03-26 02:00:00',
-            'Expected' => [
+            'start' => '2021-03-26 02:00:00',
+            'expected' => [
                 '2021-03-26 02:00:00',
                 '2022-03-26 02:00:00',
                 '2023-03-26 03:00:00',
@@ -1173,8 +1173,8 @@ public function dstYearlyTransitionProvider(): iterable
             ],
         ];
         yield 'During transition' => [
-            'Start' => '2021-03-26 02:15:00',
-            'Expected' => [
+            'start' => '2021-03-26 02:15:00',
+            'expected' => [
                 '2021-03-26 02:15:00',
                 '2022-03-26 02:15:00',
                 '2023-03-26 03:15:00',
@@ -1183,8 +1183,8 @@ public function dstYearlyTransitionProvider(): iterable
             ],
         ];
         yield 'On transition end' => [
-            'Start' => '2021-03-26 03:00:00',
-            'Expected' => [
+            'start' => '2021-03-26 03:00:00',
+            'expected' => [
                 '2021-03-26 03:00:00',
                 '2022-03-26 03:00:00',
                 '2023-03-26 03:00:00',
@@ -1193,8 +1193,8 @@ public function dstYearlyTransitionProvider(): iterable
             ],
         ];
         yield 'After transition end' => [
-            'Start' => '2021-03-26 03:15:00',
-            'Expected' => [
+            'start' => '2021-03-26 03:15:00',
+            'expected' => [
                 '2021-03-26 03:15:00',
                 '2022-03-26 03:15:00',
                 '2023-03-26 03:15:00',
@@ -1427,7 +1427,7 @@ public function testYearlyStartDateNotOnRRuleList(string $rule, string $start, a
         $this->parse($rule, $start, $expected);
     }
 
-    public function yearlyStartDateNotOnRRuleListProvider(): array
+    public static function yearlyStartDateNotOnRRuleListProvider(): array
     {
         return [
             [
diff --git a/tests/VObject/Splitter/ICalendarTest.php b/tests/VObject/Splitter/ICalendarTest.php
index f5428e937..be913780a 100644
--- a/tests/VObject/Splitter/ICalendarTest.php
+++ b/tests/VObject/Splitter/ICalendarTest.php
@@ -94,6 +94,7 @@ public function testICalendarImportInvalidEvent(): void
 
     public function testICalendarImportMultipleValidEvents(): void
     {
+        $event = [];
         $event[] = <<<EOT
 BEGIN:VEVENT
 UID:foo1
@@ -169,10 +170,10 @@ public function testICalendarImportEventWithoutUID(): void
 
         if ($messages) {
             $messages = array_map(
-                function ($item) { return $item['message']; },
+                fn ($item) => $item['message'],
                 $messages
             );
-            $this->fail('Validation errors: '.implode("\n", $messages));
+            self::fail('Validation errors: '.implode("\n", $messages));
         } else {
             self::assertEquals([], $messages);
         }
@@ -217,6 +218,7 @@ public function testICalendarImportMultipleVTIMEZONESAndMultipleValidEvents(): v
 END:VTIMEZONE
 EOT;
 
+        $event = [];
         $event[] = <<<EOT
 BEGIN:VEVENT
 UID:foo1
diff --git a/tests/VObject/Splitter/VCardTest.php b/tests/VObject/Splitter/VCardTest.php
index 7ebb07b95..a7070098e 100644
--- a/tests/VObject/Splitter/VCardTest.php
+++ b/tests/VObject/Splitter/VCardTest.php
@@ -10,7 +10,7 @@ class VCardTest extends TestCase
     public function createStream($data)
     {
         $stream = fopen('php://memory', 'r+');
-        fwrite($stream, $data);
+        fwrite($stream, (string) $data);
         rewind($stream);
 
         return $stream;
@@ -37,6 +37,7 @@ public function testVCardImportValidVCard(): void
     public function testVCardImportWrongType(): void
     {
         $this->expectException(ParseException::class);
+        $event = [];
         $event[] = <<<EOT
 BEGIN:VEVENT
 UID:foo1
diff --git a/tests/VObject/TimeZoneUtilTest.php b/tests/VObject/TimeZoneUtilTest.php
index 462218e9b..9bbf0b0c4 100644
--- a/tests/VObject/TimeZoneUtilTest.php
+++ b/tests/VObject/TimeZoneUtilTest.php
@@ -20,15 +20,15 @@ public function testCorrectTZ(string $timezoneName): void
             $tz = new \DateTimeZone($timezoneName);
             self::assertInstanceOf('DateTimeZone', $tz);
         } catch (\Exception $e) {
-            if (false !== strpos($e->getMessage(), 'Unknown or bad timezone')) {
-                $this->markTestSkipped($timezoneName.' is not (yet) supported in this PHP version. Update pecl/timezonedb');
+            if (str_contains($e->getMessage(), 'Unknown or bad timezone')) {
+                self::markTestSkipped($timezoneName.' is not (yet) supported in this PHP version. Update pecl/timezonedb');
             } else {
                 throw $e;
             }
         }
     }
 
-    public function getMapping(): array
+    public static function getMapping(): array
     {
         $map = array_merge(
             include __DIR__.'/../../lib/timezonedata/windowszones.php',
@@ -39,9 +39,7 @@ public function getMapping(): array
 
         // PHPUNit requires an array of arrays
         return array_map(
-            function ($value) {
-                return [$value];
-            },
+            fn ($value) => [$value],
             $map
         );
     }
@@ -189,8 +187,8 @@ public function testTimeZoneBCIdentifiers(string $tzid): void
          * that should be released in Feb 2023.
          */
         $versionOfPHP = \phpversion();
-        if ((('8.1.14' == $versionOfPHP) || ('8.2.1' == $versionOfPHP)) && \str_contains($tzid, '+')) {
-            $this->markTestSkipped("Timezone ids containing '+' do not work on PHP $versionOfPHP");
+        if ((('8.1.14' === $versionOfPHP) || ('8.2.1' === $versionOfPHP)) && \str_contains($tzid, '+')) {
+            self::markTestSkipped("Timezone ids containing '+' do not work on PHP $versionOfPHP");
         }
         $tz = TimeZoneUtil::getTimeZone($tzid);
         $ex = new \DateTimeZone($tzid);
@@ -198,24 +196,20 @@ public function testTimeZoneBCIdentifiers(string $tzid): void
         self::assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function getPHPTimeZoneIdentifiers(): array
+    public static function getPHPTimeZoneIdentifiers(): array
     {
         // PHPUNit requires an array of arrays
         return array_map(
-            function ($value) {
-                return [$value];
-            },
+            fn ($value) => [$value],
             \DateTimeZone::listIdentifiers()
         );
     }
 
-    public function getPHPTimeZoneBCIdentifiers(): array
+    public static function getPHPTimeZoneBCIdentifiers(): array
     {
         // PHPUNit requires an array of arrays
         return array_map(
-            function ($value) {
-                return [$value];
-            },
+            fn ($value) => [$value],
             include __DIR__.'/../../lib/timezonedata/php-bc.php'
         );
     }
diff --git a/tests/VObject/TimezoneGuesser/FindFromTimezoneMapTest.php b/tests/VObject/TimezoneGuesser/FindFromTimezoneMapTest.php
index abda23823..05ebd267c 100644
--- a/tests/VObject/TimezoneGuesser/FindFromTimezoneMapTest.php
+++ b/tests/VObject/TimezoneGuesser/FindFromTimezoneMapTest.php
@@ -23,7 +23,7 @@ public function testUpdatedTimezonesResolve(string $mapKey, string $expectedOlso
         self::assertSame($expectedOlson, $tz->getName());
     }
 
-    public function updatedTimezoneProvider(): array
+    public static function updatedTimezoneProvider(): array
     {
         return [
             // windowszones.php
diff --git a/tests/VObject/VCardConverterTest.php b/tests/VObject/VCardConverterTest.php
index bb52be8a9..cff394fe5 100644
--- a/tests/VObject/VCardConverterTest.php
+++ b/tests/VObject/VCardConverterTest.php
@@ -14,21 +14,21 @@ class VCardConverterTest extends TestCase
      */
     public function testConvert30to40(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:3.0
-PRODID:foo
-FN;CHARSET=UTF-8:Steve
-TEL;TYPE=PREF,HOME:+1 555 666 777
-ITEM1.TEL:+1 444 555 666
-ITEM1.X-ABLABEL:CustomLabel
-PHOTO;ENCODING=b;TYPE=JPEG,HOME:Zm9v
-PHOTO;ENCODING=b;TYPE=GIF:Zm9v
-PHOTO;X-PARAM=FOO;ENCODING=b;TYPE=PNG:Zm9v
-PHOTO;VALUE=URI:http://example.org/foo.png
-X-ABShowAs:COMPANY
-END:VCARD
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:3.0
+        PRODID:foo
+        FN;CHARSET=UTF-8:Steve
+        TEL;TYPE=PREF,HOME:+1 555 666 777
+        ITEM1.TEL:+1 444 555 666
+        ITEM1.X-ABLABEL:CustomLabel
+        PHOTO;ENCODING=b;TYPE=JPEG,HOME:Zm9v
+        PHOTO;ENCODING=b;TYPE=GIF:Zm9v
+        PHOTO;X-PARAM=FOO;ENCODING=b;TYPE=PNG:Zm9v
+        PHOTO;VALUE=URI:http://example.org/foo.png
+        X-ABShowAs:COMPANY
+        END:VCARD
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -60,18 +60,18 @@ public function testConvert30to40(): void
      */
     public function testConvert40to40(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:4.0
-FN:Steve
-TEL;PREF=1;TYPE=HOME:+1 555 666 777
-PHOTO:data:image/jpeg;base64,Zm9v
-PHOTO:data:image/gif;base64,Zm9v
-PHOTO;X-PARAM=FOO:data:image/png;base64,Zm9v
-PHOTO:http://example.org/foo.png
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        FN:Steve
+        TEL;PREF=1;TYPE=HOME:+1 555 666 777
+        PHOTO:data:image/jpeg;base64,Zm9v
+        PHOTO:data:image/gif;base64,Zm9v
+        PHOTO;X-PARAM=FOO:data:image/png;base64,Zm9v
+        PHOTO:http://example.org/foo.png
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -101,19 +101,19 @@ public function testConvert40to40(): void
      */
     public function testConvert21to40(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:2.1
-N:Family;Johnson
-FN:Johnson Family
-TEL;HOME;VOICE:555-12345-345
-ADR;HOME:;;100 Street Lane;Saubel Beach;ON;H0H0H0
-LABEL;HOME;ENCODING=QUOTED-PRINTABLE:100 Street Lane=0D=0ASaubel Beach,
- ON H0H0H0
-REV:20110731T040251Z
-UID:12345678
-END:VCARD
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:2.1
+        N:Family;Johnson
+        FN:Johnson Family
+        TEL;HOME;VOICE:555-12345-345
+        ADR;HOME:;;100 Street Lane;Saubel Beach;ON;H0H0H0
+        LABEL;HOME;ENCODING=QUOTED-PRINTABLE:100 Street Lane=0D=0ASaubel Beach,
+         ON H0H0H0
+        REV:20110731T040251Z
+        UID:12345678
+        END:VCARD
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -143,19 +143,19 @@ public function testConvert21to40(): void
      */
     public function testConvert30to30(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:3.0
-PRODID:foo
-FN;CHARSET=UTF-8:Steve
-TEL;TYPE=PREF,HOME:+1 555 666 777
-PHOTO;ENCODING=b;TYPE=JPEG:Zm9v
-PHOTO;ENCODING=b;TYPE=GIF:Zm9v
-PHOTO;X-PARAM=FOO;ENCODING=b;TYPE=PNG:Zm9v
-PHOTO;VALUE=URI:http://example.org/foo.png
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:3.0
+        PRODID:foo
+        FN;CHARSET=UTF-8:Steve
+        TEL;TYPE=PREF,HOME:+1 555 666 777
+        PHOTO;ENCODING=b;TYPE=JPEG:Zm9v
+        PHOTO;ENCODING=b;TYPE=GIF:Zm9v
+        PHOTO;X-PARAM=FOO;ENCODING=b;TYPE=PNG:Zm9v
+        PHOTO;VALUE=URI:http://example.org/foo.png
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -186,20 +186,20 @@ public function testConvert30to30(): void
      */
     public function testConvert40to30(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:4.0
-PRODID:foo
-FN:Steve
-TEL;PREF=1;TYPE=HOME:+1 555 666 777
-PHOTO:data:image/jpeg;base64,Zm9v
-PHOTO:data:image/gif,foo
-PHOTO;X-PARAM=FOO:data:image/png;base64,Zm9v
-PHOTO:http://example.org/foo.png
-KIND:ORG
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        PRODID:foo
+        FN:Steve
+        TEL;PREF=1;TYPE=HOME:+1 555 666 777
+        PHOTO:data:image/jpeg;base64,Zm9v
+        PHOTO:data:image/gif,foo
+        PHOTO;X-PARAM=FOO:data:image/png;base64,Zm9v
+        PHOTO:http://example.org/foo.png
+        KIND:ORG
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -230,16 +230,16 @@ public function testConvert40to30(): void
      */
     public function testConvertGroupCard(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:3.0
-PRODID:foo
-X-ADDRESSBOOKSERVER-KIND:GROUP
-X-ADDRESSBOOKSERVER-MEMBER:mailto:someone@example.com
-X-ADDRESSBOOKSERVER-MEMBER:mailto:sometwo@example.com
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:3.0
+        PRODID:foo
+        X-ADDRESSBOOKSERVER-KIND:GROUP
+        X-ADDRESSBOOKSERVER-MEMBER:mailto:someone@example.com
+        X-ADDRESSBOOKSERVER-MEMBER:mailto:sometwo@example.com
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -286,14 +286,14 @@ public function testConvertGroupCard(): void
      */
     public function testBDAYConversion()
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:3.0
-PRODID:foo
-BDAY;X-APPLE-OMIT-YEAR=1604:1604-04-16
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:3.0
+        PRODID:foo
+        BDAY;X-APPLE-OMIT-YEAR=1604:1604-04-16
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -337,22 +337,22 @@ public function testBDAYConversion()
     public function testUnknownSourceVCardVersion(): void
     {
         $this->expectException(\InvalidArgumentException::class);
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:4.2
-PRODID:foo
-FN;CHARSET=UTF-8:Steve
-TEL;TYPE=PREF,HOME:+1 555 666 777
-ITEM1.TEL:+1 444 555 666
-ITEM1.X-ABLABEL:CustomLabel
-PHOTO;ENCODING=b;TYPE=JPEG,HOME:Zm9v
-PHOTO;ENCODING=b;TYPE=GIF:Zm9v
-PHOTO;X-PARAM=FOO;ENCODING=b;TYPE=PNG:Zm9v
-PHOTO;VALUE=URI:http://example.org/foo.png
-X-ABShowAs:COMPANY
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:4.2
+        PRODID:foo
+        FN;CHARSET=UTF-8:Steve
+        TEL;TYPE=PREF,HOME:+1 555 666 777
+        ITEM1.TEL:+1 444 555 666
+        ITEM1.X-ABLABEL:CustomLabel
+        PHOTO;ENCODING=b;TYPE=JPEG,HOME:Zm9v
+        PHOTO;ENCODING=b;TYPE=GIF:Zm9v
+        PHOTO;X-PARAM=FOO;ENCODING=b;TYPE=PNG:Zm9v
+        PHOTO;VALUE=URI:http://example.org/foo.png
+        X-ABShowAs:COMPANY
+        END:VCARD
+        
+        IN_WRAP;
 
         /** @var VCard $vcard */
         $vcard = Reader::read($input);
@@ -365,13 +365,13 @@ public function testUnknownSourceVCardVersion(): void
     public function testUnknownTargetVCardVersion()
     {
         $this->expectException(\InvalidArgumentException::class);
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:3.0
-PRODID:foo
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:3.0
+        PRODID:foo
+        END:VCARD
+        
+        IN_WRAP;
 
         /** @var VCard $vcard */
         $vcard = Reader::read($input);
@@ -383,14 +383,14 @@ public function testUnknownTargetVCardVersion()
      */
     public function testConvertIndividualCard(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:4.0
-PRODID:foo
-KIND:INDIVIDUAL
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        PRODID:foo
+        KIND:INDIVIDUAL
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<OUT
 BEGIN:VCARD
@@ -431,13 +431,13 @@ public function testConvertIndividualCard(): void
      */
     public function testAnniversary(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:4.0
-ITEM1.ANNIVERSARY:20081210
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        ITEM1.ANNIVERSARY:20081210
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<'OUT'
 BEGIN:VCARD
@@ -482,15 +482,15 @@ public function testAnniversary(): void
      */
     public function testMultipleAnniversaries(): void
     {
-        $input = <<<IN
-BEGIN:VCARD
-VERSION:4.0
-ITEM1.ANNIVERSARY:20081210
-ITEM2.ANNIVERSARY:20091210
-ITEM3.ANNIVERSARY:20101210
-END:VCARD
-
-IN;
+        $input = <<<IN_WRAP
+        BEGIN:VCARD
+        VERSION:4.0
+        ITEM1.ANNIVERSARY:20081210
+        ITEM2.ANNIVERSARY:20091210
+        ITEM3.ANNIVERSARY:20101210
+        END:VCARD
+        
+        IN_WRAP;
 
         $output = <<<'OUT'
 BEGIN:VCARD
diff --git a/tests/phpunit.xml b/tests/phpunit.xml
index 01ba374c1..6d940533a 100644
--- a/tests/phpunit.xml
+++ b/tests/phpunit.xml
@@ -1,26 +1,16 @@
-<phpunit
-  colors="true"
-  bootstrap="bootstrap.php"
-  convertErrorsToExceptions="true"
-  convertNoticesToExceptions="true"
-  convertWarningsToExceptions="true"
-  beStrictAboutTestsThatDoNotTestAnything="true"
-  beStrictAboutOutputDuringTests="true"
-  failOnRisky="true"
-  failOnWarning="true"
-  enforceTimeLimit="true"
-  >
+<?xml version="1.0"?>
+<phpunit colors="true" bootstrap="bootstrap.php" beStrictAboutTestsThatDoNotTestAnything="true" beStrictAboutOutputDuringTests="true" failOnRisky="true" failOnWarning="true" enforceTimeLimit="true" cacheDirectory=".phpunit.cache">
   <php>
     <ini name="error_reporting" value="E_ALL"/>
   </php>
-  <coverage includeUncoveredFiles="true">
-    <include>
-      <directory suffix=".php">../lib/</directory>
-    </include>
-  </coverage>
   <testsuites>
     <testsuite name="Sabre\VObject">
       <directory>.</directory>
     </testsuite>
   </testsuites>
+  <source>
+    <include>
+      <directory suffix=".php">../lib/</directory>
+    </include>
+  </source>
 </phpunit>