diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 54c05805..274764b1 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -2260,151 +2260,6 @@ parameters:
 			count: 1
 			path: src/PhpSpreadsheet/Reader/BaseReader.php
 
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:\\$rowspan has no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:readBeginning\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:readEnding\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Parameter \\#2 \\$length of function fread expects int, int\\<min, \\-1\\>\\|int\\<1, 2048\\>\\|false given\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:startsWithTag\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:startsWithTag\\(\\) has parameter \\$data with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:endsWithTag\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:endsWithTag\\(\\) has parameter \\$data with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:containsTags\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:containsTags\\(\\) has parameter \\$data with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:\\$dataArray has no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:\\$tableLevel has no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:\\$nestedColumn has no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:setTableStartColumn\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:setTableStartColumn\\(\\) has parameter \\$column with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:getTableStartColumn\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:releaseTableStartColumn\\(\\) has no return typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:flushCell\\(\\) has parameter \\$cellContent with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:flushCell\\(\\) has parameter \\$column with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:flushCell\\(\\) has parameter \\$row with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Argument of an invalid type DOMNamedNodeMap\\|null supplied for foreach, only iterables are supported\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:\\$spanEtc has no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:\\$h1Etc has no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Parameter \\#2 \\$styleValue of method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:setBorderStyle\\(\\) expects string, string\\|null given\\.$#"
-			count: 5
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Parameter \\#3 \\$subject of function str_replace expects array\\|string, string\\|null given\\.$#"
-			count: 2
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Parameter \\#1 \\$pValue of method PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Alignment\\:\\:setHorizontal\\(\\) expects string, string\\|null given\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Parameter \\#1 \\$pValue of method PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Alignment\\:\\:setVertical\\(\\) expects string, string\\|null given\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:getStyleColor\\(\\) has parameter \\$value with no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Html\\:\\:\\$borderMappings has no typehint specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Html.php
-
 		-
 			message: "#^Cannot call method getNamespaces\\(\\) on SimpleXMLElement\\|false\\.$#"
 			count: 1
diff --git a/src/PhpSpreadsheet/Reader/Html.php b/src/PhpSpreadsheet/Reader/Html.php
index fe2ea018..342ce560 100644
--- a/src/PhpSpreadsheet/Reader/Html.php
+++ b/src/PhpSpreadsheet/Reader/Html.php
@@ -123,6 +123,7 @@ class Html extends BaseReader
         ], //    Italic
     ];
 
+    /** @var array */
     protected $rowspan = [];
 
     /**
@@ -160,19 +161,19 @@ class Html extends BaseReader
         return $startWithTag && $containsTags && $endsWithTag;
     }
 
-    private function readBeginning()
+    private function readBeginning(): string
     {
         fseek($this->fileHandle, 0);
 
-        return fread($this->fileHandle, self::TEST_SAMPLE_SIZE);
+        return (string) fread($this->fileHandle, self::TEST_SAMPLE_SIZE);
     }
 
-    private function readEnding()
+    private function readEnding(): string
     {
         $meta = stream_get_meta_data($this->fileHandle);
         $filename = $meta['uri'];
 
-        $size = filesize($filename);
+        $size = (int) filesize($filename);
         if ($size === 0) {
             return '';
         }
@@ -184,20 +185,20 @@ class Html extends BaseReader
 
         fseek($this->fileHandle, $size - $blockSize);
 
-        return fread($this->fileHandle, $blockSize);
+        return (string) fread($this->fileHandle, $blockSize);
     }
 
-    private static function startsWithTag($data)
+    private static function startsWithTag(string $data): bool
     {
         return '<' === substr(trim($data), 0, 1);
     }
 
-    private static function endsWithTag($data)
+    private static function endsWithTag(string $data): bool
     {
         return '>' === substr(trim($data), -1, 1);
     }
 
-    private static function containsTags($data)
+    private static function containsTags(string $data): bool
     {
         return strlen($data) !== strlen(strip_tags($data));
     }
@@ -251,13 +252,17 @@ class Html extends BaseReader
     }
 
     //    Data Array used for testing only, should write to Spreadsheet object on completion of tests
+
+    /** @var array */
     protected $dataArray = [];
 
+    /** @var int */
     protected $tableLevel = 0;
 
+    /** @var array */
     protected $nestedColumn = ['A'];
 
-    protected function setTableStartColumn($column)
+    protected function setTableStartColumn(string $column): string
     {
         if ($this->tableLevel == 0) {
             $column = 'A';
@@ -268,18 +273,25 @@ class Html extends BaseReader
         return $this->nestedColumn[$this->tableLevel];
     }
 
-    protected function getTableStartColumn()
+    protected function getTableStartColumn(): string
     {
         return $this->nestedColumn[$this->tableLevel];
     }
 
-    protected function releaseTableStartColumn()
+    protected function releaseTableStartColumn(): string
     {
         --$this->tableLevel;
 
         return array_pop($this->nestedColumn);
     }
 
+    /**
+     * Flush cell.
+     *
+     * @param string $column
+     * @param int|string $row
+     * @param mixed $cellContent
+     */
     protected function flushCell(Worksheet $sheet, $column, $row, &$cellContent): void
     {
         if (is_string($cellContent)) {
@@ -302,7 +314,7 @@ class Html extends BaseReader
     private function processDomElementBody(Worksheet $sheet, int &$row, string &$column, string &$cellContent, DOMElement $child): void
     {
         $attributeArray = [];
-        foreach ($child->attributes as $attribute) {
+        foreach (($child->attributes ?? []) as $attribute) {
             $attributeArray[$attribute->name] = $attribute->value;
         }
 
@@ -328,11 +340,11 @@ class Html extends BaseReader
         }
     }
 
-    private static $spanEtc = ['span', 'div', 'font', 'i', 'em', 'strong', 'b'];
+    private const SPAN_ETC = ['span', 'div', 'font', 'i', 'em', 'strong', 'b'];
 
     private function processDomElementSpanEtc(Worksheet $sheet, int &$row, string &$column, string &$cellContent, DOMElement $child, array &$attributeArray): void
     {
-        if (in_array($child->nodeName, self::$spanEtc)) {
+        if (in_array((string) $child->nodeName, self::SPAN_ETC, true)) {
             if (isset($attributeArray['class']) && $attributeArray['class'] === 'comment') {
                 $sheet->getComment($column . $row)
                     ->getText()
@@ -405,11 +417,11 @@ class Html extends BaseReader
         }
     }
 
-    private static $h1Etc = ['h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'ol', 'ul', 'p'];
+    private const H1_ETC = ['h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'ol', 'ul', 'p'];
 
     private function processDomElementH1Etc(Worksheet $sheet, int &$row, string &$column, string &$cellContent, DOMElement $child, array &$attributeArray): void
     {
-        if (in_array($child->nodeName, self::$h1Etc)) {
+        if (in_array((string) $child->nodeName, self::H1_ETC, true)) {
             if ($this->tableLevel > 0) {
                 //    If we're inside a table, replace with a \n
                 $cellContent .= $cellContent ? "\n" : '';
@@ -628,6 +640,16 @@ class Html extends BaseReader
         }
     }
 
+    /**
+     * Make sure mb_convert_encoding returns string.
+     *
+     * @param mixed $result
+     */
+    private static function ensureString($result): string
+    {
+        return is_string($result) ? $result : '';
+    }
+
     /**
      * Loads PhpSpreadsheet from file into PhpSpreadsheet instance.
      *
@@ -646,7 +668,8 @@ class Html extends BaseReader
         $dom = new DOMDocument();
         // Reload the HTML file into the DOM object
         try {
-            $loaded = $dom->loadHTML(mb_convert_encoding($this->securityScanner->scanFile($pFilename), 'HTML-ENTITIES', 'UTF-8'));
+            $convert = mb_convert_encoding($this->securityScanner->scanFile($pFilename), 'HTML-ENTITIES', 'UTF-8');
+            $loaded = $dom->loadHTML(self::ensureString($convert));
         } catch (Throwable $e) {
             $loaded = false;
         }
@@ -668,7 +691,8 @@ class Html extends BaseReader
         $dom = new DOMDocument();
         //    Reload the HTML file into the DOM object
         try {
-            $loaded = $dom->loadHTML(mb_convert_encoding($this->securityScanner->scan($content), 'HTML-ENTITIES', 'UTF-8'));
+            $convert = mb_convert_encoding($this->securityScanner->scan($content), 'HTML-ENTITIES', 'UTF-8');
+            $loaded = $dom->loadHTML(self::ensureString($convert));
         } catch (Throwable $e) {
             $loaded = false;
         }
@@ -774,6 +798,7 @@ class Html extends BaseReader
             $value = explode(':', $st);
             $styleName = isset($value[0]) ? trim($value[0]) : null;
             $styleValue = isset($value[1]) ? trim($value[1]) : null;
+            $styleValueString = (string) $styleValue;
 
             if (!$styleName) {
                 continue;
@@ -782,7 +807,7 @@ class Html extends BaseReader
             switch ($styleName) {
                 case 'background':
                 case 'background-color':
-                    $styleColor = $this->getStyleColor($styleValue);
+                    $styleColor = $this->getStyleColor($styleValueString);
 
                     if (!$styleColor) {
                         continue 2;
@@ -792,7 +817,7 @@ class Html extends BaseReader
 
                     break;
                 case 'color':
-                    $styleColor = $this->getStyleColor($styleValue);
+                    $styleColor = $this->getStyleColor($styleValueString);
 
                     if (!$styleColor) {
                         continue 2;
@@ -803,27 +828,27 @@ class Html extends BaseReader
                     break;
 
                 case 'border':
-                    $this->setBorderStyle($cellStyle, $styleValue, 'allBorders');
+                    $this->setBorderStyle($cellStyle, $styleValueString, 'allBorders');
 
                     break;
 
                 case 'border-top':
-                    $this->setBorderStyle($cellStyle, $styleValue, 'top');
+                    $this->setBorderStyle($cellStyle, $styleValueString, 'top');
 
                     break;
 
                 case 'border-bottom':
-                    $this->setBorderStyle($cellStyle, $styleValue, 'bottom');
+                    $this->setBorderStyle($cellStyle, $styleValueString, 'bottom');
 
                     break;
 
                 case 'border-left':
-                    $this->setBorderStyle($cellStyle, $styleValue, 'left');
+                    $this->setBorderStyle($cellStyle, $styleValueString, 'left');
 
                     break;
 
                 case 'border-right':
-                    $this->setBorderStyle($cellStyle, $styleValue, 'right');
+                    $this->setBorderStyle($cellStyle, $styleValueString, 'right');
 
                     break;
 
@@ -849,7 +874,7 @@ class Html extends BaseReader
                     break;
 
                 case 'font-family':
-                    $cellStyle->getFont()->setName(str_replace('\'', '', $styleValue));
+                    $cellStyle->getFont()->setName(str_replace('\'', '', $styleValueString));
 
                     break;
 
@@ -868,12 +893,12 @@ class Html extends BaseReader
                     break;
 
                 case 'text-align':
-                    $cellStyle->getAlignment()->setHorizontal($styleValue);
+                    $cellStyle->getAlignment()->setHorizontal($styleValueString);
 
                     break;
 
                 case 'vertical-align':
-                    $cellStyle->getAlignment()->setVertical($styleValue);
+                    $cellStyle->getAlignment()->setVertical($styleValueString);
 
                     break;
 
@@ -900,7 +925,7 @@ class Html extends BaseReader
 
                 case 'text-indent':
                     $cellStyle->getAlignment()->setIndent(
-                        (int) str_replace(['px'], '', $styleValue)
+                        (int) str_replace(['px'], '', $styleValueString)
                     );
 
                     break;
@@ -911,15 +936,18 @@ class Html extends BaseReader
     /**
      * Check if has #, so we can get clean hex.
      *
+     * @param mixed $value
+     *
      * @return null|string
      */
     public function getStyleColor($value)
     {
+        $value = (string) $value;
         if (strpos($value ?? '', '#') === 0) {
             return substr($value, 1);
         }
 
-        return \PhpOffice\PhpSpreadsheet\Helper\Html::colourNameLookup((string) $value);
+        return \PhpOffice\PhpSpreadsheet\Helper\Html::colourNameLookup($value);
     }
 
     /**
@@ -966,7 +994,7 @@ class Html extends BaseReader
         );
     }
 
-    private static $borderMappings = [
+    private const BORDER_MAPPINGS = [
         'dash-dot' => Border::BORDER_DASHDOT,
         'dash-dot-dot' => Border::BORDER_DASHDOTDOT,
         'dashed' => Border::BORDER_DASHED,
@@ -985,7 +1013,7 @@ class Html extends BaseReader
 
     public static function getBorderMappings(): array
     {
-        return self::$borderMappings;
+        return self::BORDER_MAPPINGS;
     }
 
     /**
@@ -997,7 +1025,7 @@ class Html extends BaseReader
      */
     public function getBorderStyle($style)
     {
-        return (array_key_exists($style, self::$borderMappings)) ? self::$borderMappings[$style] : null;
+        return self::BORDER_MAPPINGS[$style] ?? null;
     }
 
     /**