diff --git a/composer.json b/composer.json
index f6f20696..7ea10715 100644
--- a/composer.json
+++ b/composer.json
@@ -84,4 +84,4 @@
             "PhpOffice\\PhpSpreadsheetTests\\": "tests/PhpSpreadsheetTests"
         }
     }
-}
+}
\ No newline at end of file
diff --git a/composer.lock b/composer.lock
index 19940ce8..a23c7f8d 100644
--- a/composer.lock
+++ b/composer.lock
@@ -3208,4 +3208,4 @@
         "ext-zlib": "*"
     },
     "platform-dev": []
-}
+}
\ No newline at end of file
diff --git a/src/PhpSpreadsheet/Writer/Xls/Parser.php b/src/PhpSpreadsheet/Writer/Xls/Parser.php
index e87d09a2..6049e328 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Parser.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Parser.php
@@ -1009,7 +1009,7 @@ class Parser
 
                 break;
             case '>':
-                if ($this->lookAhead == '=') { // it's a GE token
+                if ($this->lookAhead === '=') { // it's a GE token
                     break;
                 }
 
@@ -1018,7 +1018,7 @@ class Parser
                 break;
             case '<':
                 // it's a LE or a NE token
-                if (($this->lookAhead == '=') or ($this->lookAhead == '>')) {
+                if (($this->lookAhead === '=') or ($this->lookAhead === '>')) {
                     break;
                 }
 
@@ -1027,12 +1027,12 @@ class Parser
                 break;
             default:
                 // if it's a reference A1 or $A$1 or $A1 or A$1
-                if (preg_match('/^\$?[A-Ia-i]?[A-Za-z]\$?\d+$/', $token) and !preg_match('/\d/', $this->lookAhead) and ($this->lookAhead != ':') and ($this->lookAhead != '.') and ($this->lookAhead != '!')) {
+                if (preg_match('/^\$?[A-Ia-i]?[A-Za-z]\$?\d+$/', $token) and !preg_match('/\d/', $this->lookAhead) and ($this->lookAhead !== ':') and ($this->lookAhead !== '.') and ($this->lookAhead !== '!')) {
                     return $token;
-                } elseif (preg_match('/^' . self::REGEX_SHEET_TITLE_UNQUOTED . '(\\:' . self::REGEX_SHEET_TITLE_UNQUOTED . ')?\\!\$?[A-Ia-i]?[A-Za-z]\$?\\d+$/u', $token) and !preg_match('/\d/', $this->lookAhead) and ($this->lookAhead != ':') and ($this->lookAhead != '.')) {
+                } elseif (preg_match('/^' . self::REGEX_SHEET_TITLE_UNQUOTED . '(\\:' . self::REGEX_SHEET_TITLE_UNQUOTED . ')?\\!\$?[A-Ia-i]?[A-Za-z]\$?\\d+$/u', $token) and !preg_match('/\d/', $this->lookAhead) and ($this->lookAhead !== ':') and ($this->lookAhead !== '.')) {
                     // If it's an external reference (Sheet1!A1 or Sheet1:Sheet2!A1 or Sheet1!$A$1 or Sheet1:Sheet2!$A$1)
                     return $token;
-                } elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . '(\\:' . self::REGEX_SHEET_TITLE_QUOTED . ")?'\\!\\$?[A-Ia-i]?[A-Za-z]\\$?\\d+$/u", $token) and !preg_match('/\d/', $this->lookAhead) and ($this->lookAhead != ':') and ($this->lookAhead != '.')) {
+                } elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . '(\\:' . self::REGEX_SHEET_TITLE_QUOTED . ")?'\\!\\$?[A-Ia-i]?[A-Za-z]\\$?\\d+$/u", $token) and !preg_match('/\d/', $this->lookAhead) and ($this->lookAhead !== ':') and ($this->lookAhead !== '.')) {
                     // If it's an external reference ('Sheet1'!A1 or 'Sheet1:Sheet2'!A1 or 'Sheet1'!$A$1 or 'Sheet1:Sheet2'!$A$1)
                     return $token;
                 } elseif (preg_match('/^(\$)?[A-Ia-i]?[A-Za-z](\$)?\d+:(\$)?[A-Ia-i]?[A-Za-z](\$)?\d+$/', $token) && !preg_match('/\d/', $this->lookAhead)) {
@@ -1044,19 +1044,19 @@ class Parser
                 } elseif (preg_match("/^'" . self::REGEX_SHEET_TITLE_QUOTED . '(\\:' . self::REGEX_SHEET_TITLE_QUOTED . ")?'\\!\\$?([A-Ia-i]?[A-Za-z])?\\$?\\d+:\\$?([A-Ia-i]?[A-Za-z])?\\$?\\d+$/u", $token) and !preg_match('/\d/', $this->lookAhead)) {
                     // If it's an external range like 'Sheet1'!A1:B2 or 'Sheet1:Sheet2'!A1:B2 or 'Sheet1'!$A$1:$B$2 or 'Sheet1:Sheet2'!$A$1:$B$2
                     return $token;
-                } elseif (is_numeric($token) and (!is_numeric($token . $this->lookAhead) or ($this->lookAhead == '')) and ($this->lookAhead != '!') and ($this->lookAhead != ':')) {
+                } elseif (is_numeric($token) and (!is_numeric($token . $this->lookAhead) or ($this->lookAhead == '')) and ($this->lookAhead !== '!') and ($this->lookAhead !== ':')) {
                     // If it's a number (check that it's not a sheet name or range)
                     return $token;
-                } elseif (preg_match('/"([^"]|""){0,255}"/', $token) and $this->lookAhead != '"' and (substr_count($token, '"') % 2 == 0)) {
+                } elseif (preg_match('/"([^"]|""){0,255}"/', $token) and $this->lookAhead !== '"' and (substr_count($token, '"') % 2 == 0)) {
                     // If it's a string (of maximum 255 characters)
                     return $token;
-                } elseif (preg_match('/^#[A-Z0\\/]{3,5}[!?]{1}$/', $token) or $token == '#N/A') {
+                } elseif (preg_match('/^#[A-Z0\\/]{3,5}[!?]{1}$/', $token) or $token === '#N/A') {
                     // If it's an error code
                     return $token;
-                } elseif (preg_match("/^[A-Z0-9\xc0-\xdc\\.]+$/i", $token) and ($this->lookAhead == '(')) {
+                } elseif (preg_match("/^[A-Z0-9\xc0-\xdc\\.]+$/i", $token) and ($this->lookAhead === '(')) {
                     // if it's a function call
                     return $token;
-                } elseif (substr($token, -1) == ')') {
+                } elseif (substr($token, -1) === ')') {
                     //    It's an argument of some description (e.g. a named range),
                     //        precise nature yet to be determined
                     return $token;
@@ -1078,8 +1078,7 @@ class Parser
     {
         $this->currentCharacter = 0;
         $this->formula = $formula;
-        $this->lookAhead = isset($formula[1]) ? $formula[1]
-        : '';
+        $this->lookAhead = isset($formula[1]) ? $formula[1] : '';
         $this->advance();
         $this->parseTree = $this->condition();
 
@@ -1248,10 +1247,10 @@ class Parser
      */
     private function fact()
     {
-        if ($this->currentToken == '(') {
+        if ($this->currentToken === '(') {
             $this->advance(); // eat the "("
             $result = $this->parenthesizedExpression();
-            if ($this->currentToken != ')') {
+            if ($this->currentToken !== ')') {
                 throw new WriterException("')' token expected.");
             }
             $this->advance(); // eat the ")"
@@ -1299,7 +1298,7 @@ class Parser
             return $result;
         } elseif (is_numeric($this->currentToken)) {
             // If it's a number or a percent
-            if ($this->lookAhead == '%') {
+            if ($this->lookAhead === '%') {
                 $result = $this->createTree('ptgPercent', $this->currentToken, '');
                 $this->advance(); // Skip the percentage operator once we've pre-built that tree
             } else {
@@ -1331,9 +1330,9 @@ class Parser
         $result = ''; // initialize result
         $this->advance();
         $this->advance(); // eat the "("
-        while ($this->currentToken != ')') {
+        while ($this->currentToken !== ')') {
             if ($num_args > 0) {
-                if ($this->currentToken == ',' || $this->currentToken == ';') {
+                if ($this->currentToken === ',' || $this->currentToken === ';') {
                     $this->advance(); // eat the "," or ";"
                 } else {
                     throw new WriterException("Syntax error: comma expected in function $function, arg #{$num_args}");
diff --git a/src/PhpSpreadsheet/Writer/Xls/Workbook.php b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
index b463ce4a..41c8e64e 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Workbook.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
@@ -267,9 +267,7 @@ class Workbook extends BIFFwriter
 
         $this->xfWriters[] = $xfWriter;
 
-        $xfIndex = count($this->xfWriters) - 1;
-
-        return $xfIndex;
+        return count($this->xfWriters) - 1;
     }
 
     /**
@@ -319,7 +317,7 @@ class Workbook extends BIFFwriter
             if ($colorIndex) {
                 $this->colors[$rgb] = $colorIndex;
             } else {
-                if (count($this->colors) == 0) {
+                if (count($this->colors) === 0) {
                     $lastColor = 7;
                 } else {
                     $lastColor = end($this->colors);
@@ -437,7 +435,7 @@ class Workbook extends BIFFwriter
 
         // Prepare part 3 of the workbook global stream, what goes after the SHEET records
         $part3 = '';
-        if ($this->countryCode != -1) {
+        if ($this->countryCode !== -1) {
             $part3 .= $this->writeCountry();
         }
         $part3 .= $this->writeRecalcId();
@@ -918,7 +916,7 @@ class Workbook extends BIFFwriter
         $record = 0x0022; // Record identifier
         $length = 0x0002; // Bytes to follow
 
-        $f1904 = (Date::getExcelCalendar() == Date::CALENDAR_MAC_1904)
+        $f1904 = (Date::getExcelCalendar() === Date::CALENDAR_MAC_1904)
             ? 1
             : 0; // Flag for 1904 date system
 
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php b/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
index e3ddb03c..b9f8f99b 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
@@ -93,7 +93,7 @@ class Workbook extends WriterPart
     {
         $objWriter->startElement('workbookPr');
 
-        if (Date::getExcelCalendar() == Date::CALENDAR_MAC_1904) {
+        if (Date::getExcelCalendar() === Date::CALENDAR_MAC_1904) {
             $objWriter->writeAttribute('date1904', '1');
         }
 
@@ -225,7 +225,7 @@ class Workbook extends WriterPart
             $objWriter->startElement('sheet');
             $objWriter->writeAttribute('name', $pSheetname);
             $objWriter->writeAttribute('sheetId', $pSheetId);
-            if ($sheetState != 'visible' && $sheetState != '') {
+            if ($sheetState !== 'visible' && $sheetState != '') {
                 $objWriter->writeAttribute('state', $sheetState);
             }
             $objWriter->writeAttribute('r:id', 'rId' . $pRelId);
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
index 7f48a6c1..b39ca2c2 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
@@ -141,7 +141,7 @@ class Worksheet extends WriterPart
         $objWriter->startElement('sheetPr');
         if ($pSheet->getParent()->hasMacros()) {
             //if the workbook have macros, we need to have codeName for the sheet
-            if ($pSheet->hasCodeName() == false) {
+            if (!$pSheet->hasCodeName()) {
                 $pSheet->setCodeName($pSheet->getTitle());
             }
             $objWriter->writeAttribute('codeName', $pSheet->getCodeName());
@@ -322,7 +322,7 @@ class Worksheet extends WriterPart
         }
 
         // Set Zero Height row
-        if ((string) $pSheet->getDefaultRowDimension()->getZeroHeight() == '1' ||
+        if ((string) $pSheet->getDefaultRowDimension()->getZeroHeight() === '1' ||
             strtolower((string) $pSheet->getDefaultRowDimension()->getZeroHeight()) == 'true') {
             $objWriter->writeAttribute('zeroHeight', '1');
         }
@@ -428,7 +428,7 @@ class Worksheet extends WriterPart
         // sheetProtection
         $objWriter->startElement('sheetProtection');
 
-        if ($pSheet->getProtection()->getPassword() != '') {
+        if ($pSheet->getProtection()->getPassword() !== '') {
             $objWriter->writeAttribute('password', $pSheet->getProtection()->getPassword());
         }
 
@@ -627,7 +627,7 @@ class Worksheet extends WriterPart
                     $objWriter->writeAttribute('location', str_replace('sheet://', '', $hyperlink->getUrl()));
                 }
 
-                if ($hyperlink->getTooltip() != '') {
+                if ($hyperlink->getTooltip() !== '') {
                     $objWriter->writeAttribute('tooltip', $hyperlink->getTooltip());
                     $objWriter->writeAttribute('display', $hyperlink->getTooltip());
                 }
@@ -995,12 +995,12 @@ class Worksheet extends WriterPart
                 }
 
                 // Row visibility
-                if ($rowDimension->getVisible() == false) {
+                if (!$rowDimension->getVisible()) {
                     $objWriter->writeAttribute('hidden', 'true');
                 }
 
                 // Collapsed
-                if ($rowDimension->getCollapsed() == true) {
+                if ($rowDimension->getCollapsed()) {
                     $objWriter->writeAttribute('collapsed', 'true');
                 }
 
@@ -1105,7 +1105,7 @@ class Worksheet extends WriterPart
                     break;
                 case 'f':            // Formula
                     $attributes = $pCell->getFormulaAttributes();
-                    if ($attributes['t'] == 'array') {
+                    if ($attributes['t'] === 'array') {
                         $objWriter->startElement('f');
                         $objWriter->writeAttribute('t', 'array');
                         $objWriter->writeAttribute('ref', $pCellAddress);
@@ -1118,7 +1118,7 @@ class Worksheet extends WriterPart
                     }
                     if ($this->getParentWriter()->getOffice2003Compatibility() === false) {
                         if ($this->getParentWriter()->getPreCalculateFormulas()) {
-                            if (!is_array($calculatedValue) && substr($calculatedValue, 0, 1) != '#') {
+                            if (!is_array($calculatedValue) && substr($calculatedValue, 0, 1) !== '#') {
                                 $objWriter->writeElement('v', StringHelper::formatNumber($calculatedValue));
                             } else {
                                 $objWriter->writeElement('v', '0');
@@ -1139,7 +1139,7 @@ class Worksheet extends WriterPart
 
                     break;
                 case 'e':            // Error
-                    if (substr($cellValue, 0, 1) == '=') {
+                    if (substr($cellValue, 0, 1) === '=') {
                         $objWriter->writeElement('f', substr($cellValue, 1));
                         $objWriter->writeElement('v', substr($cellValue, 1));
                     } else {