diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 000000000..f95a950f7
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,7 @@
+/tests export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore
+/.php_cs.dist export-ignore
+/.travis.yml export-ignore
+/CHANGELOG.md export-ignore
+/phpstan.neon export-ignore
diff --git a/.github/workflows/actions.yml b/.github/workflows/actions.yml
index 55ad1fb4b..7d143be0b 100644
--- a/.github/workflows/actions.yml
+++ b/.github/workflows/actions.yml
@@ -35,9 +35,17 @@ jobs:
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
           restore-keys: ${{ runner.os }}-composer-
 
-      - name: Install dependencies
+      - name: Install composer dependencies
         run: composer install --no-progress --prefer-dist --optimize-autoloader
 
+      - name: Code Analysis (PHP CS-Fixer)
+        if: matrix.code-analysis == 'yes'
+        run: php vendor/bin/php-cs-fixer fix --dry-run --diff
+
+      - name: Code Analysis (PHPStan)
+        if: matrix.code-analysis == 'yes'
+        run: composer phpstan
+
       - name: Test with phpunit
         run: vendor/bin/phpunit --configuration ./tests/phpunit.xml --coverage-text --coverage-clover=coverage.xml
 
@@ -49,4 +57,4 @@ jobs:
           flags: tests
           name: codecov-umbrella
           yml: ./codecov.yml
-          fail_ci_if_error: true
\ No newline at end of file
+          fail_ci_if_error: true
diff --git a/.gitignore b/.gitignore
index b952f0309..4b72e7ad6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,7 @@ bin/hoa
 
 # OS X
 .DS_Store
+=======
+
+# Development stuff
+.php_cs.cache
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 58921b307..b01f32d2f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,10 @@
 ChangeLog
 =========
 
+4.7.0 (2021-12-15)
+------------------
+* #34 Merge upstream changes from sabre-io/vobject:4.4.0 into protonlabs/vobject
+
 4.6.1 (2021-11-04)
 ------------------
 * #29 Fix timezone name prefixed with /
@@ -138,7 +142,7 @@ ChangeLog
 * #306: iTip REPLYs to the first instance of a recurring event was not handled
   correctly.
 * Slightly better error message during validation of `N` and `ADR` properties.
-* #312: Correctly extracing timezone in the iTip broker, even when we don't
+* #312: Correctly extracting timezone in the iTip broker, even when we don't
   have a master event. (@vkomrakov-sugar).
 * When validating a component's property that must appear once and which could
   automatically be repaired, make sure we report the change as 'repaired'.
@@ -460,7 +464,7 @@ ChangeLog
 * #114: VTIMEZONE is retained when generating new REQUEST objects.
 * #114: Support for 'MAILTO:' style email addresses (in uppercase) in the iTip
   broker. This improves evolution support.
-* #115: Using REQUEST-STATUS from REPLY messages and now propegating that into
+* #115: Using REQUEST-STATUS from REPLY messages and now propagating that into
   SCHEDULE-STATUS.
 
 
@@ -697,7 +701,7 @@ ChangeLog
 3.0.0-alpha2 (2013-05-22)
 -------------------------
 
-* Fixed: vCard URL properties were referencing a non-existant class.
+* Fixed: vCard URL properties were referencing a non-existent class.
 
 
 3.0.0-alpha1 (2013-05-21)
@@ -855,7 +859,7 @@ ChangeLog
   properties such as N, ADR, ORG and CATEGORIES.
 * Added: Splitter classes, that can split up large objects (such as exports)
   into individual objects (thanks @DominikTo and @armin-hackmann).
-* Added: VFREEBUSY component, which allows easily checking wether timeslots are
+* Added: VFREEBUSY component, which allows easily checking whether timeslots are
   available.
 * Added: The Reader class now has a 'FORGIVING' option, which allows it to parse
   properties with incorrect characters in the name (at this time, it just allows
diff --git a/README.md b/README.md
index 968bc32b9..b5b1cc96c 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ sabre/vobject
 The VObject library allows you to easily parse and manipulate [iCalendar](https://tools.ietf.org/html/rfc5545)
 and [vCard](https://tools.ietf.org/html/rfc6350) objects using PHP.
 
-The goal of the VObject library is to create a very complete library, with an easy to use API.
+The goal of the VObject library is to create a very complete library, with an easy-to-use API.
 
 
 Installation
diff --git a/bin/bench_freebusygenerator.php b/bin/bench_freebusygenerator.php
index 1299c14fb..963623d18 100644
--- a/bin/bench_freebusygenerator.php
+++ b/bin/bench_freebusygenerator.php
@@ -11,7 +11,7 @@
     echo "The process will be repeated 100 times to get accurate stats\n";
     echo "\n";
     echo 'Usage: '.$argv[0]." inputfile.ics\n";
-    die();
+    exit();
 }
 
 list(, $inputFile) = $argv;
diff --git a/bin/bench_manipulatevcard.php b/bin/bench_manipulatevcard.php
index f229091db..df6d9f23d 100644
--- a/bin/bench_manipulatevcard.php
+++ b/bin/bench_manipulatevcard.php
@@ -10,7 +10,7 @@
     echo 'system.';
     echo "\n";
     echo 'Usage: '.$argv[0]." inputfile.vcf\n";
-    die();
+    exit();
 }
 
 list(, $inputFile) = $argv;
diff --git a/bin/fetch_windows_zones.php b/bin/fetch_windows_zones.php
index 9c4e51abd..2361dc309 100755
--- a/bin/fetch_windows_zones.php
+++ b/bin/fetch_windows_zones.php
@@ -1,13 +1,12 @@
 #!/usr/bin/env php
 <?php
 
-$windowsZonesUrl = 'http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml';
+$windowsZonesUrl = 'https://raw.githubusercontent.com/unicode-org/cldr/master/common/supplemental/windowsZones.xml';
 $outputFile = __DIR__.'/../lib/timezonedata/windowszones.php';
 
 echo 'Fetching timezone map from: '.$windowsZonesUrl, "\n";
 
 $data = file_get_contents($windowsZonesUrl);
-
 $xml = simplexml_load_string($data);
 
 $map = [];
@@ -44,6 +43,6 @@
 
 echo "Formatting\n";
 
-exec(__DIR__.'/sabre-cs-fixer fix '.escapeshellarg($outputFile));
+exec(__DIR__.'/../vendor/bin/php-cs-fixer fix '.escapeshellarg($outputFile));
 
 echo "Done\n";
diff --git a/bin/generateicalendardata.php b/bin/generateicalendardata.php
index 62b6107c5..019ed9745 100755
--- a/bin/generateicalendardata.php
+++ b/bin/generateicalendardata.php
@@ -18,7 +18,7 @@
 
 HI
     );
-    die();
+    exit();
 }
 
 $events = 100;
@@ -77,7 +77,7 @@
 if ($result) {
     fwrite(STDERR, "Errors!\n");
     fwrite(STDERR, print_r($result, true));
-    die(-1);
+    exit(-1);
 }
 
 fwrite(STDERR, "Serializing this beast\n");
diff --git a/bin/mergeduplicates.php b/bin/mergeduplicates.php
index e6cde73dd..31b2c14ab 100755
--- a/bin/mergeduplicates.php
+++ b/bin/mergeduplicates.php
@@ -19,7 +19,7 @@
 
 if (!class_exists('Sabre\\VObject\\Version')) {
     fwrite(STDERR, "Composer autoloader could not be loaded.\n");
-    die(1);
+    exit(1);
 }
 
 echo 'sabre/vobject ', Version::VERSION, " duplicate contact merge tool\n";
@@ -27,7 +27,7 @@
 if ($argc < 3) {
     echo "\n";
     echo 'Usage: ', $argv[0], " input.vcf output.vcf [debug.log]\n";
-    die(1);
+    exit(1);
 }
 
 $input = fopen($argv[1], 'r');
diff --git a/bin/rrulebench.php b/bin/rrulebench.php
index 583da574c..69008002e 100644
--- a/bin/rrulebench.php
+++ b/bin/rrulebench.php
@@ -9,7 +9,7 @@
     echo 'system.';
     echo "\n";
     echo 'Usage: '.$argv[0]." inputfile.ics startdate enddate\n";
-    die();
+    exit();
 }
 
 list(, $inputFile, $startDate, $endDate) = $argv;
diff --git a/composer.json b/composer.json
index e4a0b4389..5ab1e094d 100644
--- a/composer.json
+++ b/composer.json
@@ -37,8 +37,9 @@
         "sabre/xml"    : "^2.1"
     },
     "require-dev" : {
-        "friendsofphp/php-cs-fixer": "~2.16.7",
+        "friendsofphp/php-cs-fixer": "~2.17.1",
         "phpunit/phpunit" : "^7.5 || ^8.5 || ^9.0",
+        "phpunit/php-invoker" : "^2.0 || ^3.1",
         "phpstan/phpstan": "^0.12"
     },
     "suggest" : {
diff --git a/lib/Cli.php b/lib/Cli.php
index f3e419b15..816e2cb31 100644
--- a/lib/Cli.php
+++ b/lib/Cli.php
@@ -2,8 +2,7 @@
 
 namespace Sabre\VObject;
 
-use
-    InvalidArgumentException;
+use InvalidArgumentException;
 
 /**
  * This is the CLI interface for sabre-vobject.
@@ -137,17 +136,14 @@ public function main(array $argv)
                             // 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/vcad
                             case 'icalendar':
                             case 'vcard':
@@ -183,7 +179,6 @@ public function main(array $argv)
                             case 'vcard30':
                             case 'vcard40':
                             case 'icalendar20':
-
                                 $this->inputFormat = 'mimedir';
                                 break;
 
@@ -211,7 +206,7 @@ public function main(array $argv)
             }
 
             if (!in_array($positional[0], ['validate', 'repair', 'convert', 'color'])) {
-                throw new InvalidArgumentException('Uknown command: '.$positional[0]);
+                throw new InvalidArgumentException('Unknown command: '.$positional[0]);
             }
         } catch (InvalidArgumentException $e) {
             $this->showHelp();
@@ -458,8 +453,6 @@ protected function convert($vObj)
      * Colorizes a file.
      *
      * @param Component $vObj
-     *
-     * @return int
      */
     protected function color($vObj)
     {
diff --git a/lib/Component.php b/lib/Component.php
index da45eb29f..f33b628a7 100644
--- a/lib/Component.php
+++ b/lib/Component.php
@@ -160,9 +160,9 @@ public function remove($item)
                     return;
                 }
             }
-        }
 
-        throw new \InvalidArgumentException('The item you passed to remove() was not a child of this component');
+            throw new \InvalidArgumentException('The item you passed to remove() was not a child of this component');
+        }
     }
 
     /**
@@ -339,6 +339,7 @@ function ($a, $b) use ($sortScore, $tmp) {
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $components = [];
diff --git a/lib/Component/VCalendar.php b/lib/Component/VCalendar.php
index 40e09a1c0..4db318135 100644
--- a/lib/Component/VCalendar.php
+++ b/lib/Component/VCalendar.php
@@ -309,7 +309,7 @@ public function expand(DateTimeInterface $start, DateTimeInterface $end, DateTim
 
         foreach ($this->children() as $child) {
             if ($child instanceof Property && 'PRODID' !== $child->name) {
-                // We explictly want to ignore PRODID, because we want to
+                // We explicitly want to ignore PRODID, because we want to
                 // overwrite it with our own.
                 $newChildren[] = clone $child;
             } elseif ($child instanceof Component && 'VTIMEZONE' !== $child->name) {
diff --git a/lib/Component/VCard.php b/lib/Component/VCard.php
index 51321949f..eac789842 100644
--- a/lib/Component/VCard.php
+++ b/lib/Component/VCard.php
@@ -373,7 +373,7 @@ public function getValidationRules()
     /**
      * Returns a preferred field.
      *
-     * VCards can indicate wether a field such as ADR, TEL or EMAIL is
+     * VCards can indicate whether a field such as ADR, TEL or EMAIL is
      * preferred by specifying TYPE=PREF (vcard 2.1, 3) or PREF=x (vcard 4, x
      * being a number between 1 and 100).
      *
@@ -445,6 +445,7 @@ protected function getDefaults()
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         // A vcard does not have sub-components, so we're overriding this
diff --git a/lib/ElementList.php b/lib/ElementList.php
index 56058cbd5..860512649 100644
--- a/lib/ElementList.php
+++ b/lib/ElementList.php
@@ -25,6 +25,7 @@ class ElementList extends ArrayIterator
      * @param int   $offset
      * @param mixed $value
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         throw new LogicException('You can not add new objects to an ElementList');
@@ -37,6 +38,7 @@ public function offsetSet($offset, $value)
      *
      * @param int $offset
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         throw new LogicException('You can not remove objects from an ElementList');
diff --git a/lib/FreeBusyData.php b/lib/FreeBusyData.php
index d05dfc799..4d9f441ce 100644
--- a/lib/FreeBusyData.php
+++ b/lib/FreeBusyData.php
@@ -84,7 +84,7 @@ public function add($start, $end, $type)
             'type' => $type,
         ];
 
-        $preceedingItem = $this->data[$insertStartIndex - 1];
+        $precedingItem = $this->data[$insertStartIndex - 1];
         if ($this->data[$insertStartIndex - 1]['start'] === $start) {
             // The old item starts at the exact same point as the new item.
             --$insertStartIndex;
@@ -122,11 +122,11 @@ public function add($start, $end, $type)
         // between.
         if (-1 === $itemsToDelete) {
             $itemsToDelete = 0;
-            if ($newItem['end'] < $preceedingItem['end']) {
+            if ($newItem['end'] < $precedingItem['end']) {
                 $newItems[] = [
                     'start' => $newItem['end'] + 1,
-                    'end' => $preceedingItem['end'],
-                    'type' => $preceedingItem['type'],
+                    'end' => $precedingItem['end'],
+                    'type' => $precedingItem['type'],
                 ];
             }
         }
diff --git a/lib/FreeBusyGenerator.php b/lib/FreeBusyGenerator.php
index a1c24044c..81b8126d5 100644
--- a/lib/FreeBusyGenerator.php
+++ b/lib/FreeBusyGenerator.php
@@ -126,7 +126,7 @@ public function setVAvailability(Document $vcalendar)
     /**
      * Sets the input objects.
      *
-     * You must either specify a valendar object as a string, or as the parse
+     * You must either specify a vcalendar object as a string, or as the parse
      * Component.
      * It's also possible to specify multiple objects as an array.
      *
@@ -362,7 +362,6 @@ protected function calculateBusy(FreeBusyData $fbData, array $objects)
             foreach ($object->getBaseComponents() as $component) {
                 switch ($component->name) {
                     case 'VEVENT':
-
                         $FBTYPE = 'BUSY';
                         if (isset($component->TRANSP) && ('TRANSPARENT' === strtoupper($component->TRANSP))) {
                             break;
diff --git a/lib/ITip/Broker.php b/lib/ITip/Broker.php
index 4e0368e13..b66a59f54 100644
--- a/lib/ITip/Broker.php
+++ b/lib/ITip/Broker.php
@@ -547,9 +547,13 @@ protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo,
                 // properties changed in the event, or simply if there's a
                 // difference in instances that the attendee is invited to.
 
+                $oldAttendeeInstances = array_keys($attendee['oldInstances']);
+                $newAttendeeInstances = array_keys($attendee['newInstances']);
+
                 $message->significantChange =
                     'REQUEST' === $attendee['forceSend'] ||
-                    array_keys($attendee['oldInstances']) != array_keys($attendee['newInstances']) ||
+                    count($oldAttendeeInstances) != count($newAttendeeInstances) ||
+                    count(array_diff($oldAttendeeInstances, $newAttendeeInstances)) > 0 ||
                     $oldEventInfo['significantChangeHash'] !== $eventInfo['significantChangeHash'];
 
                 foreach ($attendee['newInstances'] as $instanceId => $instanceInfo) {
@@ -816,7 +820,10 @@ protected function parseEventInfo(VCalendar $calendar = null)
         $instances = [];
         $exdate = [];
 
+        $significantChangeEventProperties = [];
+
         foreach ($calendar->VEVENT as $vevent) {
+            $eventSignificantChangeHash = '';
             $rrule = [];
 
             if (is_null($uid)) {
@@ -930,19 +937,26 @@ protected function parseEventInfo(VCalendar $calendar = null)
                 if (isset($vevent->$prop)) {
                     $propertyValues = $vevent->select($prop);
 
-                    $significantChangeHash .= $prop.':';
+                    $eventSignificantChangeHash .= $prop.':';
 
                     if ('EXDATE' === $prop) {
-                        $significantChangeHash .= implode(',', $exdate).';';
+                        $eventSignificantChangeHash .= implode(',', $exdate).';';
                     } elseif ('RRULE' === $prop) {
-                        $significantChangeHash .= implode(',', $rrule).';';
+                        $eventSignificantChangeHash .= implode(',', $rrule).';';
                     } else {
                         foreach ($propertyValues as $val) {
-                            $significantChangeHash .= $val->getValue().';';
+                            $eventSignificantChangeHash .= $val->getValue().';';
                         }
                     }
                 }
             }
+            $significantChangeEventProperties[] = $eventSignificantChangeHash;
+        }
+
+        asort($significantChangeEventProperties);
+
+        foreach ($significantChangeEventProperties as $eventSignificantChangeHash) {
+            $significantChangeHash .= $eventSignificantChangeHash;
         }
         $significantChangeHash = md5($significantChangeHash);
 
diff --git a/lib/Node.php b/lib/Node.php
index 4c0c04f72..2041b2ac7 100644
--- a/lib/Node.php
+++ b/lib/Node.php
@@ -73,6 +73,7 @@ abstract public function serialize();
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     abstract public function jsonSerialize();
 
     /**
@@ -102,6 +103,7 @@ public function destroy()
      *
      * @return ElementList
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         if (!is_null($this->iterator)) {
@@ -157,6 +159,7 @@ public function validate($options = 0)
      *
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         $it = $this->getIterator();
@@ -177,6 +180,7 @@ public function count()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         $iterator = $this->getIterator();
@@ -193,6 +197,7 @@ public function offsetExists($offset)
      *
      * @return mixed
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         $iterator = $this->getIterator();
@@ -208,6 +213,7 @@ public function offsetGet($offset)
      * @param int   $offset
      * @param mixed $value
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         $iterator = $this->getIterator();
@@ -228,6 +234,7 @@ public function offsetSet($offset, $value)
      *
      * @param int $offset
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         $iterator = $this->getIterator();
diff --git a/lib/Parameter.php b/lib/Parameter.php
index e39d320a1..7e4d55743 100644
--- a/lib/Parameter.php
+++ b/lib/Parameter.php
@@ -95,13 +95,11 @@ public static function guessParameterNameByValue($value)
             case 'WORK':
             case 'HOME':
             case 'PREF':
-
             // Delivery Label Type
             case 'DOM':
             case 'INTL':
             case 'POSTAL':
             case 'PARCEL':
-
             // Telephone types
             case 'VOICE':
             case 'FAX':
@@ -113,7 +111,6 @@ public static function guessParameterNameByValue($value)
             case 'CAR':
             case 'ISDN':
             case 'VIDEO':
-
             // EMAIL types (lol)
             case 'AOL':
             case 'APPLELINK':
@@ -127,7 +124,6 @@ public static function guessParameterNameByValue($value)
             case 'PRODIGY':
             case 'TLX':
             case 'X400':
-
             // Photo / Logo format types
             case 'GIF':
             case 'CGM':
@@ -143,12 +139,10 @@ public static function guessParameterNameByValue($value)
             case 'MPEG2':
             case 'AVI':
             case 'QTIME':
-
             // Sound Digital Audio Type
             case 'WAVE':
             case 'PCM':
             case 'AIFF':
-
             // Key types
             case 'X509':
             case 'PGP':
@@ -299,7 +293,7 @@ function ($out, $item) {
                 // https://tools.ietf.org/html/rfc6868
                 //
                 // But we've found that iCal (7.0, shipped with OSX 10.9)
-                // severaly trips on + characters not being quoted, so we
+                // severely trips on + characters not being quoted, so we
                 // added + as well.
                 if (!preg_match('#(?: [\n":;\^,\+] )#x', $item)) {
                     return $out.$item;
@@ -327,6 +321,7 @@ function ($out, $item) {
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->value;
@@ -360,6 +355,7 @@ public function __toString()
      *
      * @return ElementList
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         if (!is_null($this->iterator)) {
diff --git a/lib/Parser/MimeDir.php b/lib/Parser/MimeDir.php
index 9b36df6a9..ecf1944fa 100644
--- a/lib/Parser/MimeDir.php
+++ b/lib/Parser/MimeDir.php
@@ -343,7 +343,7 @@ protected function readProperty($line)
             ) (?=[;:,])
             /xi";
 
-        //echo $regex, "\n"; die();
+        //echo $regex, "\n"; exit();
         preg_match_all($regex, $line, $matches, PREG_SET_ORDER);
 
         $property = [
@@ -439,7 +439,7 @@ protected function readProperty($line)
             $propObj->add(null, $namelessParameter);
         }
 
-        if ('QUOTED-PRINTABLE' === strtoupper($propObj['ENCODING'])) {
+        if (isset($propObj['ENCODING']) && 'QUOTED-PRINTABLE' === strtoupper($propObj['ENCODING'])) {
             $propObj->setQuotedPrintableValue($this->extractQuotedPrintableValue());
         } else {
             $charset = $this->charset;
diff --git a/lib/Property.php b/lib/Property.php
index f9cf8e38e..6219c9b67 100644
--- a/lib/Property.php
+++ b/lib/Property.php
@@ -276,6 +276,7 @@ public function setJsonValue(array $value)
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $parameters = [];
@@ -387,6 +388,7 @@ public function __toString()
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($name)
     {
         if (is_int($name)) {
@@ -413,6 +415,7 @@ public function offsetExists($name)
      *
      * @return Node
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($name)
     {
         if (is_int($name)) {
@@ -433,6 +436,7 @@ public function offsetGet($name)
      * @param string $name
      * @param mixed  $value
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($name, $value)
     {
         if (is_int($name)) {
@@ -453,6 +457,7 @@ public function offsetSet($name, $value)
      *
      * @param string $name
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($name)
     {
         if (is_int($name)) {
diff --git a/lib/Property/Boolean.php b/lib/Property/Boolean.php
index 9fb2bce35..4bd6ffdfe 100644
--- a/lib/Property/Boolean.php
+++ b/lib/Property/Boolean.php
@@ -2,8 +2,7 @@
 
 namespace Sabre\VObject\Property;
 
-use
-    Sabre\VObject\Property;
+use Sabre\VObject\Property;
 
 /**
  * Boolean property.
diff --git a/lib/Property/ICalendar/CalAddress.php b/lib/Property/ICalendar/CalAddress.php
index e89bb31f9..86be66c15 100644
--- a/lib/Property/ICalendar/CalAddress.php
+++ b/lib/Property/ICalendar/CalAddress.php
@@ -2,8 +2,7 @@
 
 namespace Sabre\VObject\Property\ICalendar;
 
-use
-    Sabre\VObject\Property\Text;
+use Sabre\VObject\Property\Text;
 
 /**
  * CalAddress property.
diff --git a/lib/Property/ICalendar/DateTime.php b/lib/Property/ICalendar/DateTime.php
index 9342bc46e..cbafc16ba 100644
--- a/lib/Property/ICalendar/DateTime.php
+++ b/lib/Property/ICalendar/DateTime.php
@@ -184,7 +184,7 @@ public function setDateTime(DateTimeInterface $dt, $isFloating = false)
      * Sets the property as multiple date-time objects.
      *
      * The first value will be used as a reference for the timezones, and all
-     * the otehr values will be adjusted for that timezone
+     * the other values will be adjusted for that timezone
      *
      * @param DateTimeInterface[] $dt
      * @param bool isFloating If set to true, timezones will be ignored
@@ -300,6 +300,7 @@ function ($item) {
      * @param string $name
      * @param mixed  $value
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($name, $value)
     {
         parent::offsetSet($name, $value);
diff --git a/lib/Property/IntegerValue.php b/lib/Property/IntegerValue.php
index 6f709bfff..3ae775214 100644
--- a/lib/Property/IntegerValue.php
+++ b/lib/Property/IntegerValue.php
@@ -2,8 +2,7 @@
 
 namespace Sabre\VObject\Property;
 
-use
-    Sabre\VObject\Property;
+use Sabre\VObject\Property;
 
 /**
  * Integer property.
diff --git a/lib/Property/VCard/LanguageTag.php b/lib/Property/VCard/LanguageTag.php
index 697273989..318ea0231 100644
--- a/lib/Property/VCard/LanguageTag.php
+++ b/lib/Property/VCard/LanguageTag.php
@@ -2,8 +2,7 @@
 
 namespace Sabre\VObject\Property\VCard;
 
-use
-    Sabre\VObject\Property;
+use Sabre\VObject\Property;
 
 /**
  * LanguageTag property.
diff --git a/lib/Recur/EventIterator.php b/lib/Recur/EventIterator.php
index fd904b383..310bebe41 100644
--- a/lib/Recur/EventIterator.php
+++ b/lib/Recur/EventIterator.php
@@ -83,7 +83,7 @@ class EventIterator implements \Iterator
      * 2. You can pass an array of VEVENTs (all UIDS should match).
      * 3. You can pass a single VEVENT component.
      *
-     * Only the second method is recomended. The other 1 and 3 will be removed
+     * Only the second method is recommended. The other 1 and 3 will be removed
      * at some point in the future.
      *
      * The $uid parameter is only required for the first method.
@@ -229,9 +229,13 @@ public function getDtEnd()
         if (!$this->valid()) {
             return;
         }
-        $end = clone $this->currentDate;
+        if ($this->currentOverriddenEvent && $this->currentOverriddenEvent->DTEND) {
+            return $this->currentOverriddenEvent->DTEND->getDateTime($this->timeZone);
+        } else {
+            $end = clone $this->currentDate;
 
-        return $end->modify('+'.$this->eventDuration.' seconds');
+            return $end->modify('+'.$this->eventDuration.' seconds');
+        }
     }
 
     /**
diff --git a/lib/Recur/RRuleIterator.php b/lib/Recur/RRuleIterator.php
index 1607183b1..3dd483429 100644
--- a/lib/Recur/RRuleIterator.php
+++ b/lib/Recur/RRuleIterator.php
@@ -644,6 +644,13 @@ protected function nextMonthly($amount = 1)
             $currentMinuteOfMonth = 0;
             $currentSecondOfMonth = 0;
 
+            // For some reason the "until" parameter was not being used here,
+            // that's why the workaround of the 10000 year bug was needed at all
+            // let's stop it before the "until" parameter date
+            if ($this->until && $this->currentDate->getTimestamp() >= $this->until->getTimestamp()) {
+                return;
+            }
+
             // To prevent running this forever (better: until we hit the max date of DateTimeImmutable) we simply
             // stop at 9999-12-31. Looks like the year 10000 problem is not solved in php ....
             if ($this->currentDate->getTimestamp() > 253402300799) {
@@ -715,7 +722,7 @@ protected function nextYearly($amount = 1)
                     foreach ($this->byWeekNo as $byWeekNo) {
                         foreach ($dayOffsets as $dayOffset) {
                             $date = clone $this->currentDate;
-                            $date->setISODate($currentYear, $byWeekNo, $dayOffset);
+                            $date = $date->setISODate($currentYear, $byWeekNo, $dayOffset);
 
                             if ($date > $this->currentDate) {
                                 $checkDates[] = $date;
@@ -913,7 +920,6 @@ protected function parseRRule($rrule)
                     break;
 
                 case 'INTERVAL':
-
                 case 'COUNT':
                     $val = (int) $value;
                     if ($val < 1) {
@@ -1092,7 +1098,7 @@ protected function getMonthlyOccurrences()
             foreach ($this->byMonthDay as $monthDay) {
                 // Removing values that are out of range for this month
                 if ($monthDay > $startDate->format('t') ||
-                $monthDay < 0 - $startDate->format('t')) {
+                    $monthDay < 0 - $startDate->format('t')) {
                     continue;
                 }
                 if ($monthDay > 0) {
diff --git a/lib/TimeZoneUtil.php b/lib/TimeZoneUtil.php
index d1f6c344a..9e382c655 100644
--- a/lib/TimeZoneUtil.php
+++ b/lib/TimeZoneUtil.php
@@ -2,6 +2,16 @@
 
 namespace Sabre\VObject;
 
+use DateTimeZone;
+use InvalidArgumentException;
+use Sabre\VObject\TimezoneGuesser\FindFromOffset;
+use Sabre\VObject\TimezoneGuesser\FindFromTimezoneIdentifier;
+use Sabre\VObject\TimezoneGuesser\FindFromTimezoneMap;
+use Sabre\VObject\TimezoneGuesser\GuessFromLicEntry;
+use Sabre\VObject\TimezoneGuesser\GuessFromMsTzId;
+use Sabre\VObject\TimezoneGuesser\TimezoneFinder;
+use Sabre\VObject\TimezoneGuesser\TimezoneGuesser;
+
 /**
  * Time zone name translation.
  *
@@ -14,17 +24,125 @@
  */
 class TimeZoneUtil
 {
+    /** @var self */
+    private static $instance = null;
+
+    /** @var TimezoneGuesser[] */
+    private $timezoneGuessers = [];
+
+    /** @var TimezoneFinder[] */
+    private $timezoneFinders = [];
+
+    // Keeping things for backwards compatibility
+    /**
+     * @var array|null
+     *
+     * @deprecated
+     */
     public static $map = null;
 
+    private function __construct()
+    {
+        $this->addGuesser('lic', new GuessFromLicEntry());
+        $this->addGuesser('msTzId', new GuessFromMsTzId());
+        $this->addFinder('tzid', new FindFromTimezoneIdentifier());
+        $this->addFinder('tzmap', new FindFromTimezoneMap());
+        $this->addFinder('offset', new FindFromOffset());
+    }
+
+    private static function getInstance(): self
+    {
+        if (null === self::$instance) {
+            self::$instance = new self();
+        }
+
+        return self::$instance;
+    }
+
+    private function addGuesser(string $key, TimezoneGuesser $guesser): void
+    {
+        $this->timezoneGuessers[$key] = $guesser;
+    }
+
+    private function addFinder(string $key, TimezoneFinder $finder): void
+    {
+        $this->timezoneFinders[$key] = $finder;
+    }
+
+    /**
+     * This method will try to find out the correct timezone for an iCalendar
+     * date-time value.
+     *
+     * You must pass the contents of the TZID parameter, as well as the full
+     * calendar.
+     *
+     * If the lookup fails, this method will return the default PHP timezone
+     * (as configured using date_default_timezone_set, or the date.timezone ini
+     * setting).
+     *
+     * Alternatively, if $failIfUncertain is set to true, it will throw an
+     * exception if we cannot accurately determine the timezone.
+     */
+    private function findTimeZone(string $tzid, Component $vcalendar = null, bool $failIfUncertain = false): DateTimeZone
+    {
+        foreach ($this->timezoneFinders as $timezoneFinder) {
+            $timezone = $timezoneFinder->find($tzid, $failIfUncertain);
+            if (!$timezone instanceof DateTimeZone) {
+                continue;
+            }
+
+            return $timezone;
+        }
+
+        if ($vcalendar) {
+            // If that didn't work, we will scan VTIMEZONE objects
+            foreach ($vcalendar->select('VTIMEZONE') as $vtimezone) {
+                if ((string) $vtimezone->TZID === $tzid) {
+                    foreach ($this->timezoneGuessers as $timezoneGuesser) {
+                        $timezone = $timezoneGuesser->guess($vtimezone, $failIfUncertain);
+                        if (!$timezone instanceof DateTimeZone) {
+                            continue;
+                        }
+
+                        return $timezone;
+                    }
+                }
+            }
+        }
+
+        if ($failIfUncertain) {
+            throw new InvalidArgumentException('We were unable to determine the correct PHP timezone for tzid: '.$tzid);
+        }
+
+        // If we got all the way here, we default to whatever has been set as the PHP default timezone.
+        return new DateTimeZone(date_default_timezone_get());
+    }
+
+    public static function addTimezoneGuesser(string $key, TimezoneGuesser $guesser): void
+    {
+        self::getInstance()->addGuesser($key, $guesser);
+    }
+
+    public static function addTimezoneFinder(string $key, TimezoneFinder $finder): void
+    {
+        self::getInstance()->addFinder($key, $finder);
+    }
+
+    public static function clean(): void
+    {
+        self::$instance = null;
+    }
+
     /**
      * List of microsoft exchange timezone ids.
      *
      * Source: http://msdn.microsoft.com/en-us/library/aa563018(loband).aspx
+     *
+     * @deprecated
      */
     public static $microsoftExchangeMap = [
         0 => 'UTC',
         31 => 'Africa/Casablanca',
-
         // Insanely, id #2 is used for both Europe/Lisbon, and Europe/Sarajevo.
         // I'm not even kidding.. We handle this special case in the
         // getTimeZone method.
@@ -104,6 +222,7 @@ class TimeZoneUtil
     ];
 
     /**
+<<<<<<< HEAD
      * This method will try to find out the correct timezone for an iCalendar
      * date-time value.
      *
@@ -136,7 +255,7 @@ public static function getTimeZone($tzid, Component $vcalendar = null, $failIfUn
         // this method will return just GMT+01:00. This is wrong, because it
         // doesn't take DST into account.
         $originalTzid = $tzid;
-        if ('(' !== $tzid[0]) {
+        if ($tzid && '(' !== $tzid[0]) {
             // If the timezone is prefixed with a slash we remove the slash for lookup in the maps.
             if ('/' === $tzid[0]) {
                 $tzid = substr($tzid, 1);
@@ -238,8 +357,12 @@ public static function getTimeZone($tzid, Component $vcalendar = null, $failIfUn
     }
 
     /**
+=======
+>>>>>>> upstream/master
      * This method will load in all the tz mapping information, if it's not yet
      * done.
+     *
+     * @deprecated
      */
     public static function loadTzMaps()
     {
@@ -266,6 +389,8 @@ public static function loadTzMaps()
      * (See timezonedata/php-bc.php and timezonedata php-workaround.php)
      *
      * @return array
+     *
+     * @deprecated
      */
     public static function getIdentifiersBC()
     {
diff --git a/lib/TimezoneGuesser/FindFromOffset.php b/lib/TimezoneGuesser/FindFromOffset.php
new file mode 100644
index 000000000..990ac9692
--- /dev/null
+++ b/lib/TimezoneGuesser/FindFromOffset.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabre\VObject\TimezoneGuesser;
+
+use DateTimeZone;
+
+/**
+ * Some clients add 'X-LIC-LOCATION' with the olson name.
+ */
+class FindFromOffset implements TimezoneFinder
+{
+    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    {
+        // Maybe the author was hyper-lazy and just included an offset. We
+        // support it, but we aren't happy about it.
+        if (preg_match('/^GMT(\+|-)([0-9]{4})$/', $tzid, $matches)) {
+            // Note that the path in the source will never be taken from PHP 5.5.10
+            // onwards. PHP 5.5.10 supports the "GMT+0100" style of format, so it
+            // already gets returned early in this function. Once we drop support
+            // for versions under PHP 5.5.10, this bit can be taken out of the
+            // source.
+            // @codeCoverageIgnoreStart
+            return new DateTimeZone('Etc/GMT'.$matches[1].ltrim(substr($matches[2], 0, 2), '0'));
+            // @codeCoverageIgnoreEnd
+        }
+
+        return null;
+    }
+}
diff --git a/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
new file mode 100644
index 000000000..d8c6d5d3b
--- /dev/null
+++ b/lib/TimezoneGuesser/FindFromTimezoneIdentifier.php
@@ -0,0 +1,71 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabre\VObject\TimezoneGuesser;
+
+use DateTimeZone;
+use Exception;
+
+/**
+ * Some clients add 'X-LIC-LOCATION' with the olson name.
+ */
+class FindFromTimezoneIdentifier implements TimezoneFinder
+{
+    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    {
+        // First we will just see if the tzid is a support timezone identifier.
+        //
+        // The only exception is if the timezone starts with (. This is to
+        // handle cases where certain microsoft products generate timezone
+        // identifiers that for instance look like:
+        //
+        // (GMT+01.00) Sarajevo/Warsaw/Zagreb
+        //
+        // Since PHP 5.5.10, the first bit will be used as the timezone and
+        // this method will return just GMT+01:00. This is wrong, because it
+        // doesn't take DST into account
+        if (!isset($tzid[0])) {
+            return null;
+        }
+        if ('(' === $tzid[0]) {
+            return null;
+        }
+        // PHP has a bug that logs PHP warnings even it shouldn't:
+        // https://bugs.php.net/bug.php?id=67881
+        //
+        // That's why we're checking if we'll be able to successfully instantiate
+        // \DateTimeZone() before doing so. Otherwise we could simply instantiate
+        // and catch the exception.
+        $tzIdentifiers = DateTimeZone::listIdentifiers();
+
+        try {
+            if (
+                (in_array($tzid, $tzIdentifiers)) ||
+                (preg_match('/^GMT(\+|-)([0-9]{4})$/', $tzid, $matches)) ||
+                (in_array($tzid, $this->getIdentifiersBC()))
+            ) {
+                return new DateTimeZone($tzid);
+            }
+        } catch (Exception $e) {
+        }
+
+        return null;
+    }
+
+    /**
+     * This method returns an array of timezone identifiers, that are supported
+     * by DateTimeZone(), but not returned by DateTimeZone::listIdentifiers().
+     *
+     * We're not using DateTimeZone::listIdentifiers(DateTimeZone::ALL_WITH_BC) because:
+     * - It's not supported by some PHP versions as well as HHVM.
+     * - It also returns identifiers, that are invalid values for new DateTimeZone() on some PHP versions.
+     * (See timezonedata/php-bc.php and timezonedata php-workaround.php)
+     *
+     * @return array
+     */
+    private function getIdentifiersBC()
+    {
+        return include __DIR__.'/../timezonedata/php-bc.php';
+    }
+}
diff --git a/lib/TimezoneGuesser/FindFromTimezoneMap.php b/lib/TimezoneGuesser/FindFromTimezoneMap.php
new file mode 100644
index 000000000..b52ba6a19
--- /dev/null
+++ b/lib/TimezoneGuesser/FindFromTimezoneMap.php
@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabre\VObject\TimezoneGuesser;
+
+use DateTimeZone;
+
+/**
+ * Some clients add 'X-LIC-LOCATION' with the olson name.
+ */
+class FindFromTimezoneMap implements TimezoneFinder
+{
+    private $map = [];
+
+    private $patterns = [
+        '/^\((UTC|GMT)(\+|\-)[\d]{2}\:[\d]{2}\) (.*)/',
+        '/^\((UTC|GMT)(\+|\-)[\d]{2}\.[\d]{2}\) (.*)/',
+    ];
+
+    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone
+    {
+        // Next, we check if the tzid is somewhere in our tzid map.
+        if ($this->hasTzInMap($tzid)) {
+            return new DateTimeZone($this->getTzFromMap($tzid));
+        }
+
+        // Some Microsoft products prefix the offset first, so let's strip that off
+        // and see if it is our tzid map.  We don't want to check for this first just
+        // in case there are overrides in our tzid map.
+        foreach ($this->patterns as $pattern) {
+            if (!preg_match($pattern, $tzid, $matches)) {
+                continue;
+            }
+            $tzidAlternate = $matches[3];
+            if ($this->hasTzInMap($tzidAlternate)) {
+                return new DateTimeZone($this->getTzFromMap($tzidAlternate));
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * This method returns an array of timezone identifiers, that are supported
+     * by DateTimeZone(), but not returned by DateTimeZone::listIdentifiers().
+     *
+     * We're not using DateTimeZone::listIdentifiers(DateTimeZone::ALL_WITH_BC) because:
+     * - It's not supported by some PHP versions as well as HHVM.
+     * - It also returns identifiers, that are invalid values for new DateTimeZone() on some PHP versions.
+     * (See timezonedata/php-bc.php and timezonedata php-workaround.php)
+     *
+     * @return array
+     */
+    private function getTzMaps()
+    {
+        if ([] === $this->map) {
+            $this->map = array_merge(
+                include __DIR__.'/../timezonedata/windowszones.php',
+                include __DIR__.'/../timezonedata/lotuszones.php',
+                include __DIR__.'/../timezonedata/exchangezones.php',
+                include __DIR__.'/../timezonedata/php-workaround.php'
+            );
+        }
+
+        return $this->map;
+    }
+
+    private function getTzFromMap(string $tzid): string
+    {
+        return $this->getTzMaps()[$tzid];
+    }
+
+    private function hasTzInMap(string $tzid): bool
+    {
+        return isset($this->getTzMaps()[$tzid]);
+    }
+}
diff --git a/lib/TimezoneGuesser/GuessFromLicEntry.php b/lib/TimezoneGuesser/GuessFromLicEntry.php
new file mode 100644
index 000000000..f340a3962
--- /dev/null
+++ b/lib/TimezoneGuesser/GuessFromLicEntry.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabre\VObject\TimezoneGuesser;
+
+use DateTimeZone;
+use Sabre\VObject\Component\VTimeZone;
+use Sabre\VObject\TimeZoneUtil;
+
+/**
+ * Some clients add 'X-LIC-LOCATION' with the olson name.
+ */
+class GuessFromLicEntry implements TimezoneGuesser
+{
+    public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?DateTimeZone
+    {
+        if (!isset($vtimezone->{'X-LIC-LOCATION'})) {
+            return null;
+        }
+
+        $lic = (string) $vtimezone->{'X-LIC-LOCATION'};
+
+        // Libical generators may specify strings like
+        // "SystemV/EST5EDT". For those we must remove the
+        // SystemV part.
+        if ('SystemV/' === substr($lic, 0, 8)) {
+            $lic = substr($lic, 8);
+        }
+
+        return TimeZoneUtil::getTimeZone($lic, null, $failIfUncertain);
+    }
+}
diff --git a/lib/TimezoneGuesser/GuessFromMsTzId.php b/lib/TimezoneGuesser/GuessFromMsTzId.php
new file mode 100644
index 000000000..b11ce1832
--- /dev/null
+++ b/lib/TimezoneGuesser/GuessFromMsTzId.php
@@ -0,0 +1,119 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabre\VObject\TimezoneGuesser;
+
+use DateTimeZone;
+use Sabre\VObject\Component\VTimeZone;
+
+class GuessFromMsTzId implements TimezoneGuesser
+{
+    /**
+     * List of microsoft exchange timezone ids.
+     *
+     * Source: http://msdn.microsoft.com/en-us/library/aa563018(loband).aspx
+     */
+    public static $microsoftExchangeMap = [
+        0 => 'UTC',
+        31 => 'Africa/Casablanca',
+
+        // Insanely, id #2 is used for both Europe/Lisbon, and Europe/Sarajevo.
+        // I'm not even kidding.. We handle this special case in the
+        // getTimeZone method.
+        2 => 'Europe/Lisbon',
+        1 => 'Europe/London',
+        4 => 'Europe/Berlin',
+        6 => 'Europe/Prague',
+        3 => 'Europe/Paris',
+        69 => 'Africa/Luanda', // This was a best guess
+        7 => 'Europe/Athens',
+        5 => 'Europe/Bucharest',
+        49 => 'Africa/Cairo',
+        50 => 'Africa/Harare',
+        59 => 'Europe/Helsinki',
+        27 => 'Asia/Jerusalem',
+        26 => 'Asia/Baghdad',
+        74 => 'Asia/Kuwait',
+        51 => 'Europe/Moscow',
+        56 => 'Africa/Nairobi',
+        25 => 'Asia/Tehran',
+        24 => 'Asia/Muscat', // Best guess
+        54 => 'Asia/Baku',
+        48 => 'Asia/Kabul',
+        58 => 'Asia/Yekaterinburg',
+        47 => 'Asia/Karachi',
+        23 => 'Asia/Calcutta',
+        62 => 'Asia/Kathmandu',
+        46 => 'Asia/Almaty',
+        71 => 'Asia/Dhaka',
+        66 => 'Asia/Colombo',
+        61 => 'Asia/Rangoon',
+        22 => 'Asia/Bangkok',
+        64 => 'Asia/Krasnoyarsk',
+        45 => 'Asia/Shanghai',
+        63 => 'Asia/Irkutsk',
+        21 => 'Asia/Singapore',
+        73 => 'Australia/Perth',
+        75 => 'Asia/Taipei',
+        20 => 'Asia/Tokyo',
+        72 => 'Asia/Seoul',
+        70 => 'Asia/Yakutsk',
+        19 => 'Australia/Adelaide',
+        44 => 'Australia/Darwin',
+        18 => 'Australia/Brisbane',
+        76 => 'Australia/Sydney',
+        43 => 'Pacific/Guam',
+        42 => 'Australia/Hobart',
+        68 => 'Asia/Vladivostok',
+        41 => 'Asia/Magadan',
+        17 => 'Pacific/Auckland',
+        40 => 'Pacific/Fiji',
+        67 => 'Pacific/Tongatapu',
+        29 => 'Atlantic/Azores',
+        53 => 'Atlantic/Cape_Verde',
+        30 => 'America/Noronha',
+        8 => 'America/Sao_Paulo', // Best guess
+        32 => 'America/Argentina/Buenos_Aires',
+        60 => 'America/Godthab',
+        28 => 'America/St_Johns',
+        9 => 'America/Halifax',
+        33 => 'America/Caracas',
+        65 => 'America/Santiago',
+        35 => 'America/Bogota',
+        10 => 'America/New_York',
+        34 => 'America/Indiana/Indianapolis',
+        55 => 'America/Guatemala',
+        11 => 'America/Chicago',
+        37 => 'America/Mexico_City',
+        36 => 'America/Edmonton',
+        38 => 'America/Phoenix',
+        12 => 'America/Denver', // Best guess
+        13 => 'America/Los_Angeles', // Best guess
+        14 => 'America/Anchorage',
+        15 => 'Pacific/Honolulu',
+        16 => 'Pacific/Midway',
+        39 => 'Pacific/Kwajalein',
+    ];
+
+    public function guess(VTimeZone $vtimezone, bool $throwIfUnsure = false): ?DateTimeZone
+    {
+        // Microsoft may add a magic number, which we also have an
+        // answer for.
+        if (!isset($vtimezone->{'X-MICROSOFT-CDO-TZID'})) {
+            return null;
+        }
+        $cdoId = (int) $vtimezone->{'X-MICROSOFT-CDO-TZID'}->getValue();
+
+        // 2 can mean both Europe/Lisbon and Europe/Sarajevo.
+        if (2 === $cdoId && false !== strpos((string) $vtimezone->TZID, 'Sarajevo')) {
+            return new DateTimeZone('Europe/Sarajevo');
+        }
+
+        if (isset(self::$microsoftExchangeMap[$cdoId])) {
+            return new DateTimeZone(self::$microsoftExchangeMap[$cdoId]);
+        }
+
+        return null;
+    }
+}
diff --git a/lib/TimezoneGuesser/TimezoneFinder.php b/lib/TimezoneGuesser/TimezoneFinder.php
new file mode 100644
index 000000000..5aa880a1c
--- /dev/null
+++ b/lib/TimezoneGuesser/TimezoneFinder.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace Sabre\VObject\TimezoneGuesser;
+
+use DateTimeZone;
+
+interface TimezoneFinder
+{
+    public function find(string $tzid, bool $failIfUncertain = false): ?DateTimeZone;
+}
diff --git a/lib/TimezoneGuesser/TimezoneGuesser.php b/lib/TimezoneGuesser/TimezoneGuesser.php
new file mode 100644
index 000000000..5e193bb52
--- /dev/null
+++ b/lib/TimezoneGuesser/TimezoneGuesser.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Sabre\VObject\TimezoneGuesser;
+
+use DateTimeZone;
+use Sabre\VObject\Component\VTimeZone;
+
+interface TimezoneGuesser
+{
+    public function guess(VTimeZone $vtimezone, bool $failIfUncertain = false): ?DateTimeZone;
+}
diff --git a/lib/timezonedata/windowszones.php b/lib/timezonedata/windowszones.php
index af3904b12..2049a95c1 100644
--- a/lib/timezonedata/windowszones.php
+++ b/lib/timezonedata/windowszones.php
@@ -3,14 +3,14 @@
 /**
  * Automatically generated timezone file.
  *
- * Last update: 2016-08-24T17:35:38-04:00
- * Source: http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml
+ * Last update: 2020-12-13T17:38:12+05:45
+ * Source: https://raw.githubusercontent.com/unicode-org/cldr/master/common/supplemental/windowsZones.xml
  *
- * @copyright Copyright (C) 2011-2015 fruux GmbH (https://fruux.com/).
+ * @copyright Copyright (C) fruux GmbH (https://fruux.com/).
  * @license http://sabre.io/license/ Modified BSD License
  */
 
-return  [
+return [
   'AUS Central Standard Time' => 'Australia/Darwin',
   'AUS Eastern Standard Time' => 'Australia/Sydney',
   'Afghanistan Standard Time' => 'Asia/Kabul',
@@ -74,6 +74,7 @@
   'Line Islands Standard Time' => 'Pacific/Kiritimati',
   'Lord Howe Standard Time' => 'Australia/Lord_Howe',
   'Magadan Standard Time' => 'Asia/Magadan',
+  'Magallanes Standard Time' => 'America/Punta_Arenas',
   'Marquesas Standard Time' => 'Pacific/Marquesas',
   'Mauritius Standard Time' => 'Indian/Mauritius',
   'Middle East Standard Time' => 'Asia/Beirut',
@@ -91,11 +92,13 @@
   'North Asia East Standard Time' => 'Asia/Irkutsk',
   'North Asia Standard Time' => 'Asia/Krasnoyarsk',
   'North Korea Standard Time' => 'Asia/Pyongyang',
+  'Omsk Standard Time' => 'Asia/Omsk',
   'Pacific SA Standard Time' => 'America/Santiago',
   'Pacific Standard Time' => 'America/Los_Angeles',
   'Pacific Standard Time (Mexico)' => 'America/Tijuana',
   'Pakistan Standard Time' => 'Asia/Karachi',
   'Paraguay Standard Time' => 'America/Asuncion',
+  'Qyzylorda Standard Time' => 'Asia/Qyzylorda',
   'Romance Standard Time' => 'Europe/Paris',
   'Russia Time Zone 10' => 'Asia/Srednekolymsk',
   'Russia Time Zone 11' => 'Asia/Kamchatka',
@@ -108,9 +111,12 @@
   'Saint Pierre Standard Time' => 'America/Miquelon',
   'Sakhalin Standard Time' => 'Asia/Sakhalin',
   'Samoa Standard Time' => 'Pacific/Apia',
+  'Sao Tome Standard Time' => 'Africa/Sao_Tome',
+  'Saratov Standard Time' => 'Europe/Saratov',
   'Singapore Standard Time' => 'Asia/Singapore',
   'South Africa Standard Time' => 'Africa/Johannesburg',
   'Sri Lanka Standard Time' => 'Asia/Colombo',
+  'Sudan Standard Time' => 'Africa/Khartoum',
   'Syria Standard Time' => 'Asia/Damascus',
   'Taipei Standard Time' => 'Asia/Taipei',
   'Tasmania Standard Time' => 'Australia/Hobart',
@@ -125,6 +131,7 @@
   'US Mountain Standard Time' => 'America/Phoenix',
   'UTC' => 'Etc/GMT',
   'UTC+12' => 'Etc/GMT-12',
+  'UTC+13' => 'Etc/GMT-13',
   'UTC-02' => 'Etc/GMT+2',
   'UTC-08' => 'Etc/GMT+8',
   'UTC-09' => 'Etc/GMT+9',
@@ -132,6 +139,7 @@
   'Ulaanbaatar Standard Time' => 'Asia/Ulaanbaatar',
   'Venezuela Standard Time' => 'America/Caracas',
   'Vladivostok Standard Time' => 'Asia/Vladivostok',
+  'Volgograd Standard Time' => 'Europe/Volgograd',
   'W. Australia Standard Time' => 'Australia/Perth',
   'W. Central Africa Standard Time' => 'Africa/Lagos',
   'W. Europe Standard Time' => 'Europe/Berlin',
@@ -140,4 +148,5 @@
   'West Bank Standard Time' => 'Asia/Hebron',
   'West Pacific Standard Time' => 'Pacific/Port_Moresby',
   'Yakutsk Standard Time' => 'Asia/Yakutsk',
+  'Yukon Standard Time' => 'America/Whitehorse',
 ];
diff --git a/tests/VObject/Component/VAvailabilityTest.php b/tests/VObject/Component/VAvailabilityTest.php
index 2fd9c0dde..edd06b02b 100644
--- a/tests/VObject/Component/VAvailabilityTest.php
+++ b/tests/VObject/Component/VAvailabilityTest.php
@@ -122,7 +122,7 @@ public function testIsInTimeRangeOutside()
         );
     }
 
-    public function testRFCxxxSection3_1_availabilityprop_required()
+    public function testRFCxxxSection3Part1AvailabilitypropRequired()
     {
         // UID and DTSTAMP are present.
         $this->assertIsValid(Reader::read(
@@ -177,7 +177,7 @@ public function testRFCxxxSection3_1_availabilityprop_required()
         ));
     }
 
-    public function testRFCxxxSection3_1_availabilityprop_optional_once()
+    public function testRFCxxxSection3Part1AvailabilitypropOptionalOnce()
     {
         $properties = [
             'BUSYTYPE:BUSY',
@@ -205,7 +205,7 @@ public function testRFCxxxSection3_1_availabilityprop_optional_once()
         }
     }
 
-    public function testRFCxxxSection3_1_availabilityprop_dtend_duration()
+    public function testRFCxxxSection3Part1AvailabilitypropDtendDuration()
     {
         // Only DTEND.
         $this->assertIsValid(Reader::read($this->template([
@@ -239,7 +239,7 @@ public function testAvailableSubComponent()
         $this->assertInstanceOf(Available::class, $document->VAVAILABILITY->AVAILABLE);
     }
 
-    public function testRFCxxxSection3_1_availableprop_required()
+    public function testRFCxxxSection3Part1AvailablepropRequired()
     {
         // UID, DTSTAMP and DTSTART are present.
         $this->assertIsValid(Reader::read(
@@ -331,7 +331,7 @@ public function testRFCxxxSection3_1_availableprop_required()
         ));
     }
 
-    public function testRFCxxxSection3_1_available_dtend_duration()
+    public function testRFCxxxSection3Part1AvailableDtendDuration()
     {
         // Only DTEND.
         $this->assertIsValid(Reader::read($this->templateAvailable([
@@ -350,7 +350,7 @@ public function testRFCxxxSection3_1_available_dtend_duration()
         ])));
     }
 
-    public function testRFCxxxSection3_1_available_optional_once()
+    public function testRFCxxxSection3Part1AvailableOptionalOnce()
     {
         $properties = [
             'CREATED:20111005T135125Z',
@@ -373,7 +373,7 @@ public function testRFCxxxSection3_1_available_optional_once()
         }
     }
 
-    public function testRFCxxxSection3_2()
+    public function testRFCxxxSection3Part2()
     {
         $this->assertEquals(
             'BUSY',
diff --git a/tests/VObject/Component/VCalendarTest.php b/tests/VObject/Component/VCalendarTest.php
index c2f0ce978..d34e12d2b 100644
--- a/tests/VObject/Component/VCalendarTest.php
+++ b/tests/VObject/Component/VCalendarTest.php
@@ -350,6 +350,33 @@ public function testBrokenEventExpand()
         );
     }
 
+    /**
+     * This test used to induce an infinite loop.
+     * The "medium" annotation means that phpunit will fail the
+     * test if it takes longer than a default of 10 seconds.
+     *
+     * @medium
+     */
+    public function testEventExpandYearly()
+    {
+        $input = 'BEGIN:VCALENDAR
+BEGIN:VEVENT
+UID:1a093f1012086078fdd3d9df5ff4d7d0
+DTSTART;TZID=UTC:20210203T130000
+DTEND;TZID=UTC:20210203T140000
+RRULE:FREQ=YEARLY;COUNT=7;WKST=MO;BYDAY=MO;BYWEEKNO=13,15,50
+END:VEVENT
+END:VCALENDAR
+';
+        $vcal = VObject\Reader::read($input);
+        $events = $vcal->expand(
+            new \DateTime('2021-01-01'),
+            new \DateTime('2023-01-01')
+        );
+
+        $this->assertCount(7, $events->VEVENT);
+    }
+
     public function testGetDocumentType()
     {
         $vcard = new VCalendar();
diff --git a/tests/VObject/Component/VCardTest.php b/tests/VObject/Component/VCardTest.php
index 3124fec84..d8e6110b6 100644
--- a/tests/VObject/Component/VCardTest.php
+++ b/tests/VObject/Component/VCardTest.php
@@ -135,8 +135,8 @@ public function testGetByType()
         $vcard = VObject\Reader::read($vcard);
         $this->assertEquals('1@example.org', $vcard->getByType('EMAIL', 'home')->getValue());
         $this->assertEquals('2@example.org', $vcard->getByType('EMAIL', 'work')->getValue());
-        $this->assertNull($vcard->getByType('EMAIL', 'non-existant'));
-        $this->assertNull($vcard->getByType('ADR', 'non-existant'));
+        $this->assertNull($vcard->getByType('EMAIL', 'non-existent'));
+        $this->assertNull($vcard->getByType('ADR', 'non-existent'));
     }
 
     public function testPreferredNoPref()
diff --git a/tests/VObject/ComponentTest.php b/tests/VObject/ComponentTest.php
index f56d55531..cf3e196dc 100644
--- a/tests/VObject/ComponentTest.php
+++ b/tests/VObject/ComponentTest.php
@@ -72,6 +72,23 @@ public function testMagicGetGroups()
         $this->assertEquals(null, $email3[0]->group);
     }
 
+    public function testAddGroupProperties()
+    {
+        $comp = new VCard([
+            'VERSION' => '3.0',
+            'item2.X-ABLabel' => 'item2-Foo',
+        ]);
+
+        $comp->{'ITEM1.X-ABLabel'} = 'ITEM1-Foo';
+
+        foreach (['item2', 'ITEM1'] as $group) {
+            $prop = $comp->{"$group.X-ABLabel"};
+            $this->assertInstanceOf(Property::class, $prop);
+            $this->assertSame("$group-Foo", (string) $prop);
+            $this->assertSame($group, $prop->group);
+        }
+    }
+
     public function testMagicIsset()
     {
         $comp = new VCalendar();
diff --git a/tests/VObject/DateTimeParserTest.php b/tests/VObject/DateTimeParserTest.php
index b20a43217..ede81e321 100644
--- a/tests/VObject/DateTimeParserTest.php
+++ b/tests/VObject/DateTimeParserTest.php
@@ -408,7 +408,7 @@ public function vcardDates()
         ];
     }
 
-    public function testDateAndOrTime_DateWithYearMonthDay()
+    public function testDateAndOrTimeDateWithYearMonthDay()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '20150128',
@@ -420,7 +420,7 @@ public function testDateAndOrTime_DateWithYearMonthDay()
         );
     }
 
-    public function testDateAndOrTime_DateWithYearMonth()
+    public function testDateAndOrTimeDateWithYearMonth()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '2015-01',
@@ -431,7 +431,7 @@ public function testDateAndOrTime_DateWithYearMonth()
         );
     }
 
-    public function testDateAndOrTime_DateWithMonth()
+    public function testDateAndOrTimeDateWithMonth()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '--01',
@@ -441,7 +441,7 @@ public function testDateAndOrTime_DateWithMonth()
         );
     }
 
-    public function testDateAndOrTime_DateWithMonthDay()
+    public function testDateAndOrTimeDateWithMonthDay()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '--0128',
@@ -452,7 +452,7 @@ public function testDateAndOrTime_DateWithMonthDay()
         );
     }
 
-    public function testDateAndOrTime_DateWithDay()
+    public function testDateAndOrTimeDateWithDay()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '---28',
@@ -462,7 +462,7 @@ public function testDateAndOrTime_DateWithDay()
         );
     }
 
-    public function testDateAndOrTime_TimeWithHour()
+    public function testDateAndOrTimeTimeWithHour()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '13',
@@ -472,7 +472,7 @@ public function testDateAndOrTime_TimeWithHour()
         );
     }
 
-    public function testDateAndOrTime_TimeWithHourMinute()
+    public function testDateAndOrTimeTimeWithHourMinute()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '1353',
@@ -483,7 +483,7 @@ public function testDateAndOrTime_TimeWithHourMinute()
         );
     }
 
-    public function testDateAndOrTime_TimeWithHourSecond()
+    public function testDateAndOrTimeTimeWithHourSecond()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '135301',
@@ -495,7 +495,7 @@ public function testDateAndOrTime_TimeWithHourSecond()
         );
     }
 
-    public function testDateAndOrTime_TimeWithMinute()
+    public function testDateAndOrTimeTimeWithMinute()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '-53',
@@ -505,7 +505,7 @@ public function testDateAndOrTime_TimeWithMinute()
         );
     }
 
-    public function testDateAndOrTime_TimeWithMinuteSecond()
+    public function testDateAndOrTimeTimeWithMinuteSecond()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '-5301',
@@ -516,7 +516,7 @@ public function testDateAndOrTime_TimeWithMinuteSecond()
         );
     }
 
-    public function testDateAndOrTime_TimeWithSecond()
+    public function testDateAndOrTimeTimeWithSecond()
     {
         $this->assertTrue(true);
 
@@ -526,7 +526,7 @@ public function testDateAndOrTime_TimeWithSecond()
          */
     }
 
-    public function testDateAndOrTime_TimeWithSecondZ()
+    public function testDateAndOrTimeTimeWithSecondZ()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '--01Z',
@@ -537,7 +537,7 @@ public function testDateAndOrTime_TimeWithSecondZ()
         );
     }
 
-    public function testDateAndOrTime_TimeWithSecondTZ()
+    public function testDateAndOrTimeTimeWithSecondTZ()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '--01+1234',
@@ -548,7 +548,7 @@ public function testDateAndOrTime_TimeWithSecondTZ()
         );
     }
 
-    public function testDateAndOrTime_DateTimeWithYearMonthDayHour()
+    public function testDateAndOrTimeDateTimeWithYearMonthDayHour()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '20150128T13',
@@ -561,7 +561,7 @@ public function testDateAndOrTime_DateTimeWithYearMonthDayHour()
         );
     }
 
-    public function testDateAndOrTime_DateTimeWithMonthDayHour()
+    public function testDateAndOrTimeDateTimeWithMonthDayHour()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '--0128T13',
@@ -573,7 +573,7 @@ public function testDateAndOrTime_DateTimeWithMonthDayHour()
         );
     }
 
-    public function testDateAndOrTime_DateTimeWithDayHour()
+    public function testDateAndOrTimeDateTimeWithDayHour()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '---28T13',
@@ -584,7 +584,7 @@ public function testDateAndOrTime_DateTimeWithDayHour()
         );
     }
 
-    public function testDateAndOrTime_DateTimeWithDayHourMinute()
+    public function testDateAndOrTimeDateTimeWithDayHourMinute()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '---28T1353',
@@ -596,7 +596,7 @@ public function testDateAndOrTime_DateTimeWithDayHourMinute()
         );
     }
 
-    public function testDateAndOrTime_DateTimeWithDayHourMinuteSecond()
+    public function testDateAndOrTimeDateTimeWithDayHourMinuteSecond()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '---28T135301',
@@ -609,7 +609,7 @@ public function testDateAndOrTime_DateTimeWithDayHourMinuteSecond()
         );
     }
 
-    public function testDateAndOrTime_DateTimeWithDayHourZ()
+    public function testDateAndOrTimeDateTimeWithDayHourZ()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '---28T13Z',
@@ -621,7 +621,7 @@ public function testDateAndOrTime_DateTimeWithDayHourZ()
         );
     }
 
-    public function testDateAndOrTime_DateTimeWithDayHourTZ()
+    public function testDateAndOrTimeDateTimeWithDayHourTZ()
     {
         $this->assertDateAndOrTimeEqualsTo(
             '---28T13+1234',
diff --git a/tests/VObject/EmptyValueIssueTest.php b/tests/VObject/EmptyValueIssueTest.php
index 91a4d84f6..0798d9c4a 100644
--- a/tests/VObject/EmptyValueIssueTest.php
+++ b/tests/VObject/EmptyValueIssueTest.php
@@ -17,7 +17,7 @@ public function testDecodeValue()
 BEGIN:VCALENDAR
 VERSION:2.0
 BEGIN:VEVENT
-DESCRIPTION:This is a descpription\\nwith a linebreak and a \\; \\, and :
+DESCRIPTION:This is a description\\nwith a linebreak and a \\; \\, and :
 END:VEVENT
 END:VCALENDAR
 ICS;
@@ -25,6 +25,6 @@ public function testDecodeValue()
         $vobj = Reader::read($input);
 
         // Before this bug was fixed, getValue() would return nothing.
-        $this->assertEquals("This is a descpription\nwith a linebreak and a ; , and :", $vobj->VEVENT->DESCRIPTION->getValue());
+        $this->assertEquals("This is a description\nwith a linebreak and a ; , and :", $vobj->VEVENT->DESCRIPTION->getValue());
     }
 }
diff --git a/tests/VObject/ITip/BrokerAttendeeReplyTest.php b/tests/VObject/ITip/BrokerAttendeeReplyTest.php
index 71008c6ae..284075adf 100644
--- a/tests/VObject/ITip/BrokerAttendeeReplyTest.php
+++ b/tests/VObject/ITip/BrokerAttendeeReplyTest.php
@@ -907,7 +907,7 @@ public function testDeclinedCancelledEvent()
      * Except in this case, there was already an overridden event, and the
      * overridden event was marked as cancelled by the attendee.
      *
-     * For any other attendence status, the new status would have been
+     * For any other attendance status, the new status would have been
      * declined, but for this, no message should we sent.
      */
     public function testDontCreateReplyWhenEventWasDeclined()
diff --git a/tests/VObject/ITip/BrokerProcessReplyTest.php b/tests/VObject/ITip/BrokerProcessReplyTest.php
index 1cb685096..bbfd6c419 100644
--- a/tests/VObject/ITip/BrokerProcessReplyTest.php
+++ b/tests/VObject/ITip/BrokerProcessReplyTest.php
@@ -373,7 +373,7 @@ public function testReplyNewExceptionTz()
         $result = $this->process($itip, $old, $expected);
     }
 
-    public function testReplyPartyCrashCreateExcepton()
+    public function testReplyPartyCrashCreateException()
     {
         // IN this test there's a recurring event that has an exception. The
         // exception is missing the attendee.
diff --git a/tests/VObject/ITip/BrokerSignificantChangesTest.php b/tests/VObject/ITip/BrokerSignificantChangesTest.php
index a225cb98c..a20d55025 100644
--- a/tests/VObject/ITip/BrokerSignificantChangesTest.php
+++ b/tests/VObject/ITip/BrokerSignificantChangesTest.php
@@ -105,4 +105,112 @@ public function testSignificantChangesRRuleOrderNoChange()
 
         $this->parse($old, $new, $expected, 'mailto:martin@fruux.com');
     }
+
+    /**
+     * Check significant changes detection (no change).
+     * Reordering of the attendees should not be a significant change (#540)
+     * https://github.com/sabre-io/vobject/issues/540.
+     */
+    public function testSignificantChangesAttendeesOrderNoChange()
+    {
+        $old = <<<ICS
+BEGIN:VCALENDAR
+VERSION:2.0
+CALSCALE:GREGORIAN
+PRODID:-//Ximian//NONSGML Evolution Calendar//EN
+BEGIN:VEVENT
+UID:20140813T153116Z-12176-1000-1065-6@johnny-lubuntu
+DTSTAMP:20140813T142829Z
+DTSTART;TZID=America/Toronto:20140815T110000
+SEQUENCE:2
+SUMMARY:Evo makes a Meeting
+LOCATION:fruux HQ
+CLASS:PUBLIC
+RRULE:FREQ=WEEKLY;BYDAY=MO
+ORGANIZER:MAILTO:martin@fruux.com
+ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=
+ TRUE;LANGUAGE=en:MAILTO:dominik@fruux.com
+ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=
+ TRUE;LANGUAGE=de:MAILTO:holger@fruux.com
+CREATED:20140813T153211Z
+LAST-MODIFIED:20140813T155353Z
+END:VEVENT
+END:VCALENDAR
+ICS;
+
+        $new = str_replace('holger@fruux.com', 'dominik1@fruux.com', $old);
+        $new = str_replace('dominik@fruux.com', 'holger@fruux.com', $new);
+        $new = str_replace('dominik1@fruux.com', 'dominik@fruux.com', $new);
+        $expected = [];
+        $expected[] = ['significantChange' => false];
+        $expected[] = ['significantChange' => false];
+
+        $this->parse($old, $new, $expected, 'mailto:martin@fruux.com');
+    }
+
+    /**
+     * Check significant changes detection (no change).
+     * Reordering of vevent in a recurring event with exceptions should
+     * not be a significant change
+     * https://github.com/sabre-io/vobject/issues/542.
+     */
+    public function testSignificantChangesVeventOrderNoChange()
+    {
+        $vevent1 = <<<ICS
+BEGIN:VEVENT
+UID:20140813T153116Z-12176-1000-1065-6@johnny-lubuntu
+DTSTAMP:20140813T142829Z
+DTSTART;TZID=America/Toronto:20140815T110000
+SEQUENCE:2
+SUMMARY:Evo makes a Meeting
+LOCATION:fruux HQ
+CLASS:PUBLIC
+RRULE:FREQ=WEEKLY;BYDAY=MO
+ORGANIZER:MAILTO:martin@fruux.com
+ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=
+ TRUE;LANGUAGE=en:MAILTO:dominik@fruux.com
+CREATED:20140813T153211Z
+LAST-MODIFIED:20140813T155353Z
+END:VEVENT
+ICS;
+        // This event is slightly different. DTSTAMP is in 2021
+        $vevent2 = <<<ICS
+BEGIN:VEVENT
+UID:20140813T153116Z-12176-1000-1065-6@johnny-lubuntu
+DTSTAMP:20210813T142829Z
+DTSTART;TZID=America/Toronto:20140815T110000
+SEQUENCE:2
+SUMMARY:Evo makes a Meeting
+LOCATION:fruux HQ
+CLASS:PUBLIC
+RRULE:FREQ=WEEKLY;BYDAY=MO
+ORGANIZER:MAILTO:martin@fruux.com
+ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=
+ TRUE;LANGUAGE=en:MAILTO:dominik@fruux.com
+CREATED:20140813T153211Z
+LAST-MODIFIED:20140813T155353Z
+END:VEVENT
+ICS;
+
+        $head = <<<ICS
+BEGIN:VCALENDAR
+VERSION:2.0
+CALSCALE:GREGORIAN
+PRODID:-//Ximian//NONSGML Evolution Calendar//EN
+ICS;
+
+        $old = $head;
+        $old .= "\n".$vevent1;
+        $old .= "\n".$vevent2;
+        $old .= "\nEND:VCALENDAR";
+
+        $new = $head;
+        $new .= "\n".$vevent1;
+        $new .= "\n".$vevent2;
+        $new .= "\nEND:VCALENDAR";
+
+        $expected = [['significantChange' => false]];
+
+        $this->parse($old, $new, $expected, 'mailto:martin@fruux.com');
+    }
 }
diff --git a/tests/VObject/Parser/XmlTest.php b/tests/VObject/Parser/XmlTest.php
index e520185ba..46ee30ce2 100644
--- a/tests/VObject/Parser/XmlTest.php
+++ b/tests/VObject/Parser/XmlTest.php
@@ -262,7 +262,7 @@ public function testRFC6321Example2()
     /**
      * iCalendar Stream.
      */
-    public function testRFC6321Section3_2()
+    public function testRFC6321Section3Part2()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -280,7 +280,7 @@ public function testRFC6321Section3_2()
     /**
      * All components exist.
      */
-    public function testRFC6321Section3_3()
+    public function testRFC6321Section3Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -325,7 +325,7 @@ public function testRFC6321Section3_3()
     /**
      * Properties, Special Cases, GEO.
      */
-    public function testRFC6321Section3_4_1_2()
+    public function testRFC6321Section3Part4Part1Part2()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -351,7 +351,7 @@ public function testRFC6321Section3_4_1_2()
     /**
      * Properties, Special Cases, REQUEST-STATUS.
      */
-    public function testRFC6321Section3_4_1_3()
+    public function testRFC6321Section3Part4Part1Part3()
     {
         // Example 1 of RFC5545, Section 3.8.8.3.
         $this->assertXMLReflexivelyEqualsToMimeDir(
@@ -466,7 +466,7 @@ public function testRFC6321Section3_4_1_3()
     /**
      * Values, Binary.
      */
-    public function testRFC6321Section3_6_1()
+    public function testRFC6321Section3Part6Part1()
     {
         $this->assertXMLEqualsToMimeDir(
 <<<XML
@@ -511,7 +511,7 @@ public function testRFC6321Section3_6_1()
     /**
      * Values, Boolean.
      */
-    public function testRFC6321Section3_6_2()
+    public function testRFC6321Section3Part6Part2()
     {
         $this->assertXMLEqualsToMimeDir(
 <<<XML
@@ -539,7 +539,7 @@ public function testRFC6321Section3_6_2()
     /**
      * Values, Calendar User Address.
      */
-    public function testRFC6321Section3_6_3()
+    public function testRFC6321Section3Part6Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -564,7 +564,7 @@ public function testRFC6321Section3_6_3()
     /**
      * Values, Date.
      */
-    public function testRFC6321Section3_6_4()
+    public function testRFC6321Section3Part6Part4()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -589,7 +589,7 @@ public function testRFC6321Section3_6_4()
     /**
      * Values, Date-Time.
      */
-    public function testRFC6321Section3_6_5()
+    public function testRFC6321Section3Part6Part5()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -614,7 +614,7 @@ public function testRFC6321Section3_6_5()
     /**
      * Values, Duration.
      */
-    public function testRFC6321Section3_6_6()
+    public function testRFC6321Section3Part6Part6()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -639,16 +639,16 @@ public function testRFC6321Section3_6_6()
     /**
      * Values, Float.
      */
-    public function testRFC6321Section3_6_7()
+    public function testRFC6321Section3Part6Part7()
     {
         // GEO uses <float /> with a positive and a non-negative numbers.
-        $this->testRFC6321Section3_4_1_2();
+        $this->testRFC6321Section3Part4Part1Part2();
     }
 
     /**
      * Values, Integer.
      */
-    public function testRFC6321Section3_6_8()
+    public function testRFC6321Section3Part6Part8()
     {
         $this->assertXMLEqualsToMimeDir(
 <<<XML
@@ -692,7 +692,7 @@ public function testRFC6321Section3_6_8()
     /**
      * Values, Period of Time.
      */
-    public function testRFC6321Section3_6_9()
+    public function testRFC6321Section3Part6Part9()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -742,7 +742,7 @@ public function testRFC6321Section3_6_9()
     /**
      * Values, Recurrence Rule.
      */
-    public function testRFC6321Section3_6_10()
+    public function testRFC6321Section3Part6Part10()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -772,7 +772,7 @@ public function testRFC6321Section3_6_10()
     /**
      * Values, Text.
      */
-    public function testRFC6321Section3_6_11()
+    public function testRFC6321Section3Part6Part11()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -797,7 +797,7 @@ public function testRFC6321Section3_6_11()
     /**
      * Values, Time.
      */
-    public function testRFC6321Section3_6_12()
+    public function testRFC6321Section3Part6Part12()
     {
         $this->assertXMLEqualsToMimeDir(
 <<<XML
@@ -822,7 +822,7 @@ public function testRFC6321Section3_6_12()
     /**
      * Values, URI.
      */
-    public function testRFC6321Section3_6_13()
+    public function testRFC6321Section3Part6Part13()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -847,7 +847,7 @@ public function testRFC6321Section3_6_13()
     /**
      * Values, UTC Offset.
      */
-    public function testRFC6321Section3_6_14()
+    public function testRFC6321Section3Part6Part14()
     {
         // Example 1 of RFC5545, Section 3.3.14.
         $this->assertXMLReflexivelyEqualsToMimeDir(
@@ -1259,7 +1259,7 @@ public function testRFC6351Section5Group()
     /**
      * Extensibility.
      */
-    public function testRFC6351Section5_1_NoNamespace()
+    public function testRFC6351Section5Part1NoNamespace()
     {
         $this->assertXMLEqualsToMimeDir(
 <<<XML
@@ -1777,7 +1777,7 @@ public function testRFC6351ValueDateTimeWithDayHourTZ()
     /**
      * Property: SOURCE.
      */
-    public function testRFC6350Section6_1_3()
+    public function testRFC6350Section6Part1Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1801,7 +1801,7 @@ public function testRFC6350Section6_1_3()
     /**
      * Property: KIND.
      */
-    public function testRFC6350Section6_1_4()
+    public function testRFC6350Section6Part1Part4()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1825,7 +1825,7 @@ public function testRFC6350Section6_1_4()
     /**
      * Property: FN.
      */
-    public function testRFC6350Section6_2_1()
+    public function testRFC6350Section6Part2Part1()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1849,7 +1849,7 @@ public function testRFC6350Section6_2_1()
     /**
      * Property: N.
      */
-    public function testRFC6350Section6_2_2()
+    public function testRFC6350Section6Part2Part2()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1877,7 +1877,7 @@ public function testRFC6350Section6_2_2()
     /**
      * Property: NICKNAME.
      */
-    public function testRFC6350Section6_2_3()
+    public function testRFC6350Section6Part2Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1902,7 +1902,7 @@ public function testRFC6350Section6_2_3()
     /**
      * Property: PHOTO.
      */
-    public function testRFC6350Section6_2_4()
+    public function testRFC6350Section6Part2Part4()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1923,7 +1923,7 @@ public function testRFC6350Section6_2_4()
         );
     }
 
-    public function testRFC6350Section6_2_5()
+    public function testRFC6350Section6Part2Part5()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1944,7 +1944,7 @@ public function testRFC6350Section6_2_5()
         );
     }
 
-    public function testRFC6350Section6_2_6()
+    public function testRFC6350Section6Part2Part6()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1968,7 +1968,7 @@ public function testRFC6350Section6_2_6()
     /**
      * Property: GENDER.
      */
-    public function testRFC6350Section6_2_7()
+    public function testRFC6350Section6Part2Part7()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -1993,7 +1993,7 @@ public function testRFC6350Section6_2_7()
     /**
      * Property: ADR.
      */
-    public function testRFC6350Section6_3_1()
+    public function testRFC6350Section6Part3Part1()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2023,7 +2023,7 @@ public function testRFC6350Section6_3_1()
     /**
      * Property: TEL.
      */
-    public function testRFC6350Section6_4_1()
+    public function testRFC6350Section6Part4Part1()
     {
         /*
          * Quoting RFC:
@@ -2085,7 +2085,7 @@ public function testRFC6350Section6_4_1()
     /**
      * Property: EMAIL.
      */
-    public function testRFC6350Section6_4_2()
+    public function testRFC6350Section6Part4Part2()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2114,7 +2114,7 @@ public function testRFC6350Section6_4_2()
     /**
      * Property: IMPP.
      */
-    public function testRFC6350Section6_4_3()
+    public function testRFC6350Section6Part4Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2143,7 +2143,7 @@ public function testRFC6350Section6_4_3()
     /**
      * Property: LANG.
      */
-    public function testRFC6350Section6_4_4()
+    public function testRFC6350Section6Part4Part4()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2175,7 +2175,7 @@ public function testRFC6350Section6_4_4()
     /**
      * Property: TZ.
      */
-    public function testRFC6350Section6_5_1()
+    public function testRFC6350Section6Part5Part1()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2199,7 +2199,7 @@ public function testRFC6350Section6_5_1()
     /**
      * Property: GEO.
      */
-    public function testRFC6350Section6_5_2()
+    public function testRFC6350Section6Part5Part2()
     {
         $this->assertXMLEqualsToMimeDir(
 <<<XML
@@ -2241,7 +2241,7 @@ public function testRFC6350Section6_5_2()
     /**
      * Property: TITLE.
      */
-    public function testRFC6350Section6_6_1()
+    public function testRFC6350Section6Part6Part1()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2265,7 +2265,7 @@ public function testRFC6350Section6_6_1()
     /**
      * Property: ROLE.
      */
-    public function testRFC6350Section6_6_2()
+    public function testRFC6350Section6Part6Part2()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2289,7 +2289,7 @@ public function testRFC6350Section6_6_2()
     /**
      * Property: LOGO.
      */
-    public function testRFC6350Section6_6_3()
+    public function testRFC6350Section6Part6Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2313,7 +2313,7 @@ public function testRFC6350Section6_6_3()
     /**
      * Property: ORG.
      */
-    public function testRFC6350Section6_6_4()
+    public function testRFC6350Section6Part6Part4()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2339,7 +2339,7 @@ public function testRFC6350Section6_6_4()
     /**
      * Property: MEMBER.
      */
-    public function testRFC6350Section6_6_5()
+    public function testRFC6350Section6Part6Part5()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2393,7 +2393,7 @@ public function testRFC6350Section6_6_5()
     /**
      * Property: RELATED.
      */
-    public function testRFC6350Section6_6_6()
+    public function testRFC6350Section6Part6Part6()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2422,7 +2422,7 @@ public function testRFC6350Section6_6_6()
     /**
      * Property: CATEGORIES.
      */
-    public function testRFC6350Section6_7_1()
+    public function testRFC6350Section6Part7Part1()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2449,7 +2449,7 @@ public function testRFC6350Section6_7_1()
     /**
      * Property: NOTE.
      */
-    public function testRFC6350Section6_7_2()
+    public function testRFC6350Section6Part7Part2()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2473,7 +2473,7 @@ public function testRFC6350Section6_7_2()
     /**
      * Property: PRODID.
      */
-    public function testRFC6350Section6_7_3()
+    public function testRFC6350Section6Part7Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2494,7 +2494,7 @@ public function testRFC6350Section6_7_3()
         );
     }
 
-    public function testRFC6350Section6_7_4()
+    public function testRFC6350Section6Part7Part4()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2518,7 +2518,7 @@ public function testRFC6350Section6_7_4()
     /**
      * Property: SOUND.
      */
-    public function testRFC6350Section6_7_5()
+    public function testRFC6350Section6Part7Part5()
     {
         $this->assertXMLEqualsToMimeDir(
 <<<XML
@@ -2560,7 +2560,7 @@ public function testRFC6350Section6_7_5()
     /**
      * Property: UID.
      */
-    public function testRFC6350Section6_7_6()
+    public function testRFC6350Section6Part7Part6()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2584,7 +2584,7 @@ public function testRFC6350Section6_7_6()
     /**
      * Property: CLIENTPIDMAP.
      */
-    public function testRFC6350Section6_7_7()
+    public function testRFC6350Section6Part7Part7()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2609,7 +2609,7 @@ public function testRFC6350Section6_7_7()
     /**
      * Property: URL.
      */
-    public function testRFC6350Section6_7_8()
+    public function testRFC6350Section6Part7Part8()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2633,7 +2633,7 @@ public function testRFC6350Section6_7_8()
     /**
      * Property: VERSION.
      */
-    public function testRFC6350Section6_7_9()
+    public function testRFC6350Section6Part7Part9()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2652,7 +2652,7 @@ public function testRFC6350Section6_7_9()
     /**
      * Property: KEY.
      */
-    public function testRFC6350Section6_8_1()
+    public function testRFC6350Section6Part8Part1()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2681,7 +2681,7 @@ public function testRFC6350Section6_8_1()
     /**
      * Property: FBURL.
      */
-    public function testRFC6350Section6_9_1()
+    public function testRFC6350Section6Part9Part1()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2710,7 +2710,7 @@ public function testRFC6350Section6_9_1()
     /**
      * Property: CALADRURI.
      */
-    public function testRFC6350Section6_9_2()
+    public function testRFC6350Section6Part9Part2()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2734,7 +2734,7 @@ public function testRFC6350Section6_9_2()
     /**
      * Property: CALURI.
      */
-    public function testRFC6350Section6_9_3()
+    public function testRFC6350Section6Part9Part3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
@@ -2763,7 +2763,7 @@ public function testRFC6350Section6_9_3()
     /**
      * Property: CAPURI.
      */
-    public function testRFC6350SectionA_3()
+    public function testRFC6350SectionAPart3()
     {
         $this->assertXMLReflexivelyEqualsToMimeDir(
 <<<XML
diff --git a/tests/VObject/ReaderTest.php b/tests/VObject/ReaderTest.php
index 63d1dccf2..96ed56be0 100644
--- a/tests/VObject/ReaderTest.php
+++ b/tests/VObject/ReaderTest.php
@@ -336,7 +336,7 @@ public function testReadWithInvalidLine()
         $data = [
             'BEGIN:VCALENDAR',
             'DESCRIPTION:propValue',
-            "Yes, we've actually seen a file with non-idented property values on multiple lines",
+            "Yes, we've actually seen a file with non-indented property values on multiple lines",
             'END:VCALENDAR',
         ];
 
diff --git a/tests/VObject/Recur/EventIterator/MainTest.php b/tests/VObject/Recur/EventIterator/MainTest.php
index 1a019a57d..cf317f3ea 100644
--- a/tests/VObject/Recur/EventIterator/MainTest.php
+++ b/tests/VObject/Recur/EventIterator/MainTest.php
@@ -1172,7 +1172,7 @@ public function testComplexExclusions()
     /**
      * @depends testValues
      */
-    public function testOverridenEvent()
+    public function testOverriddenEvent()
     {
         $vcal = new VCalendar();
 
@@ -1243,7 +1243,7 @@ public function testOverridenEvent()
     /**
      * @depends testValues
      */
-    public function testOverridenEvent2()
+    public function testOverriddenEvent2()
     {
         $vcal = new VCalendar();
 
@@ -1291,7 +1291,7 @@ public function testOverridenEvent2()
     /**
      * @depends testValues
      */
-    public function testOverridenEventNoValuesExpected()
+    public function testOverriddenEventNoValuesExpected()
     {
         $vcal = new VCalendar();
         $ev1 = $vcal->createComponent('VEVENT');
@@ -1318,12 +1318,12 @@ public function testOverridenEventNoValuesExpected()
         $summaries = [];
 
         // The reported problem was specifically related to the VCALENDAR
-        // expansion. In this parcitular case, we had to forward to the 28th of
+        // expansion. In this particular case, we had to forward to the 28th of
         // january.
         $it->fastForward(new DateTimeImmutable('2012-01-28 23:00:00'));
 
-        // We stop the loop when it hits the 6th of februari. Normally this
-        // iterator would hit 24, 25 (overriden from 31) and 7 feb but because
+        // We stop the loop when it hits the 6th of February. Normally this
+        // iterator would hit 24, 25 (overridden from 31) and 7 feb but because
         // we 'filter' from the 28th till the 6th, we should get 0 results.
         while ($it->valid() && $it->getDTStart() < new DateTimeImmutable('2012-02-06 23:00:00')) {
             $dates[] = $it->getDTStart();
diff --git a/tests/VObject/Recur/EventIterator/OverrideDurationTest.php b/tests/VObject/Recur/EventIterator/OverrideDurationTest.php
new file mode 100644
index 000000000..f25ef13d9
--- /dev/null
+++ b/tests/VObject/Recur/EventIterator/OverrideDurationTest.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace Sabre\VObject\Recur\EventIterator;
+
+use PHPUnit\Framework\TestCase;
+use Sabre\VObject\Reader;
+use Sabre\VObject\Recur\EventIterator;
+
+class OverrideDurationTest extends TestCase
+{
+    use \Sabre\VObject\PHPUnitAssertions;
+
+    public function testOverrideDuration()
+    {
+        $ics = <<<ICS
+BEGIN:VCALENDAR
+BEGIN:VEVENT
+UID:1
+SUMMARY:9-10Uhr
+RRULE:FREQ=DAILY
+DTSTART;TZID=Europe/Berlin:20210517T090000
+DTEND;TZID=Europe/Berlin:20210517T100000
+END:VEVENT
+BEGIN:VEVENT
+UID:2
+SUMMARY:9-12Uhr
+DTSTART;TZID=Europe/Berlin:20210519T090000
+DTEND;TZID=Europe/Berlin:20210519T120000
+RECURRENCE-ID;TZID=Europe/Berlin:20210519T090000
+END:VEVENT
+END:VCALENDAR
+ICS;
+
+        $vCalendar = Reader::read($ics);
+        $eventIterator = new EventIterator($vCalendar->getComponents());
+
+        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-17 09:00:00', 'recur event start time');
+        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-17 10:00:00', 'recur event end time');
+
+        $eventIterator->next();
+        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-18 09:00:00', 'recur event start time');
+        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-18 10:00:00', 'recur event end time');
+
+        $eventIterator->next();
+        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-19 09:00:00', 'overridden event start time');
+        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-19 12:00:00', 'overridden event end time');
+
+        $eventIterator->next();
+        $this->assertEquals($eventIterator->current()->format('Y-m-d H:i:s'), '2021-05-20 09:00:00', 'recur event start time');
+        $this->assertEquals($eventIterator->getDtEnd()->format('Y-m-d H:i:s'), '2021-05-20 10:00:00', 'recur event end time');
+    }
+}
diff --git a/tests/VObject/Recur/RRuleIteratorTest.php b/tests/VObject/Recur/RRuleIteratorTest.php
index 5f56e6849..cd4c3f8d4 100644
--- a/tests/VObject/Recur/RRuleIteratorTest.php
+++ b/tests/VObject/Recur/RRuleIteratorTest.php
@@ -278,7 +278,7 @@ public function testMonthly()
         );
     }
 
-    public function testMonlthyEndOfMonth()
+    public function testMonthlyEndOfMonth()
     {
         $this->parse(
             'FREQ=MONTHLY;INTERVAL=2;COUNT=12',
@@ -358,6 +358,35 @@ public function testMonthlyByDay()
         );
     }
 
+    public function testMonthlyByDayUntil()
+    {
+        $this->parse(
+            'FREQ=MONTHLY;INTERVAL=1;BYDAY=WE;WKST=WE;UNTIL=20210317T000000Z',
+            '2021-02-10 00:00:00',
+            [
+                '2021-02-10 00:00:00',
+                '2021-02-17 00:00:00',
+                '2021-02-24 00:00:00',
+                '2021-03-03 00:00:00',
+                '2021-03-10 00:00:00',
+                '2021-03-17 00:00:00',
+            ],
+            'monthly', null, 1, new DateTime('2021-03-17')
+        );
+    }
+
+    public function testMonthlyByDayUntilWithImpossibleNextOccurrence()
+    {
+        $this->parse(
+            'FREQ=MONTHLY;INTERVAL=1;BYDAY=2WE;BYMONTHDAY=2;WKST=WE;UNTIL=20210317T000000Z',
+            '2021-02-10 00:00:00',
+            [
+                '2021-02-10 00:00:00',
+            ],
+            'monthly', null, 1, new DateTime('2021-03-17')
+        );
+    }
+
     public function testMonthlyByDayByMonthDay()
     {
         $this->parse(
@@ -689,6 +718,20 @@ public function testYearlyByYearDayInvalid0()
         );
     }
 
+    public function testYearlyByDayByWeekNo()
+    {
+        $this->parse(
+            'FREQ=YEARLY;COUNT=3;BYDAY=MO;BYWEEKNO=13,15,50',
+            '2021-01-01 00:00:00',
+            [
+                '2021-01-01 00:00:00',
+                '2021-03-29 00:00:00',
+                '2021-04-12 00:00:00',
+            ],
+            'yearly', 3, 1
+        );
+    }
+
     public function testFastForward()
     {
         // The idea is that we're fast-forwarding too far in the future, so
@@ -728,7 +771,7 @@ public function testFifthTuesdayProblem()
      * This bug came from a Fruux customer. This would result in a never-ending
      * request.
      */
-    public function testFastFowardTooFar()
+    public function testFastForwardTooFar()
     {
         $this->parse(
             'FREQ=WEEKLY;BYDAY=MO;UNTIL=20090704T205959Z;INTERVAL=1',
@@ -1014,6 +1057,13 @@ public function testMinusFifthThursday()
         );
     }
 
+    /**
+     * This test can take some seconds to complete.
+     * The "large" annotation means phpunit will let it run for
+     * up to 60 seconds by default.
+     *
+     * @large
+     */
     public function testNeverEnding()
     {
         $this->parse(
diff --git a/tests/VObject/TimeZoneUtilTest.php b/tests/VObject/TimeZoneUtilTest.php
index 8b6103f68..33a1eff98 100644
--- a/tests/VObject/TimeZoneUtilTest.php
+++ b/tests/VObject/TimeZoneUtilTest.php
@@ -10,6 +10,7 @@ public function setUp(): void
     {
         // clearning the tz cache
         TimeZoneUtil::$map = null;
+        TimeZoneUtil::clean();
     }
 
     /**
@@ -31,22 +32,28 @@ public function testCorrectTZ($timezoneName)
 
     public function getMapping()
     {
-        TimeZoneUtil::loadTzMaps();
+        $map = array_merge(
+            include __DIR__.'/../../lib/timezonedata/windowszones.php',
+            include __DIR__.'/../../lib/timezonedata/lotuszones.php',
+            include __DIR__.'/../../lib/timezonedata/exchangezones.php',
+            include __DIR__.'/../../lib/timezonedata/php-workaround.php'
+        );
 
         // PHPUNit requires an array of arrays
         return array_map(
             function ($value) {
                 return [$value];
             },
-            TimeZoneUtil::$map
+            $map
         );
     }
 
     /**
      * @dataProvider getMapping
      */
-    public function testSlashTZ($timezonename) {
-        $slashTimezone = '/' . $timezonename;
+    public function testSlashTZ($timezonename)
+    {
+        $slashTimezone = '/'.$timezonename;
         $expected = TimeZoneUtil::getTimeZone($timezonename)->getName();
         $actual = TimeZoneUtil::getTimeZone($slashTimezone)->getName();
         $this->assertEquals($expected, $actual);
@@ -92,7 +99,7 @@ public function testExchangeMap()
         $this->assertEquals($ex->getName(), $tz->getName());
     }
 
-    public function testWetherMicrosoftIsStillInsane()
+    public function testWhetherMicrosoftIsStillInsane()
     {
         $vobj = <<<HI
 BEGIN:VCALENDAR
@@ -157,6 +164,13 @@ public function testUnknownExchangeId()
         $this->assertEquals($ex->getName(), $tz->getName());
     }
 
+    public function testEmptyTimeZone()
+    {
+        $tz = TimeZoneUtil::getTimeZone('');
+        $ex = new \DateTimeZone('UTC');
+        $this->assertEquals($ex->getName(), $tz->getName());
+    }
+
     public function testWindowsTimeZone()
     {
         $tz = TimeZoneUtil::getTimeZone('Eastern Standard Time');
@@ -204,7 +218,7 @@ public function getPHPTimeZoneBCIdentifiers()
             function ($value) {
                 return [$value];
             },
-            TimeZoneUtil::getIdentifiersBC()
+            include __DIR__.'/../../lib/timezonedata/php-bc.php'
         );
     }