diff --git a/docs/topics/reading-files.md b/docs/topics/reading-files.md
index 35ae7ed7..5b07a81d 100644
--- a/docs/topics/reading-files.md
+++ b/docs/topics/reading-files.md
@@ -289,21 +289,21 @@ useful:
 /**  Define a Read Filter class implementing \PhpOffice\PhpSpreadsheet\Reader\IReadFilter  */
 class MyReadFilter implements \PhpOffice\PhpSpreadsheet\Reader\IReadFilter
 {
-    private $_startRow = 0;
-    private $_endRow   = 0;
-    private $_columns  = array();
+    private $startRow = 0;
+    private $endRow   = 0;
+    private $columns  = array();
 
     /**  Get the list of rows and columns to read  */
     public function __construct($startRow, $endRow, $columns) {
-        $this->_startRow = $startRow;
-        $this->_endRow   = $endRow;
-        $this->_columns  = $columns;
+        $this->startRow = $startRow;
+        $this->endRow   = $endRow;
+        $this->columns  = $columns;
     }
 
     public function readCell($column, $row, $worksheetName = '') {
         //  Only read the rows and columns that were configured
-        if ($row >= $this->_startRow && $row <= $this->_endRow) {
-            if (in_array($column,$this->_columns)) {
+        if ($row >= $this->startRow && $row <= $this->endRow) {
+            if (in_array($column,$this->columns)) {
                 return true;
             }
         }
@@ -331,18 +331,18 @@ $inputFileName = './sampleData/example2.xls';
 /**  Define a Read Filter class implementing \PhpOffice\PhpSpreadsheet\Reader\IReadFilter  */
 class ChunkReadFilter implements \PhpOffice\PhpSpreadsheet\Reader\IReadFilter
 {
-    private $_startRow = 0;
-    private $_endRow   = 0;
+    private $startRow = 0;
+    private $endRow   = 0;
 
     /**  Set the list of rows that we want to read  */
     public function setRows($startRow, $chunkSize) {
-        $this->_startRow = $startRow;
-        $this->_endRow   = $startRow + $chunkSize;
+        $this->startRow = $startRow;
+        $this->endRow   = $startRow + $chunkSize;
     }
 
     public function readCell($column, $row, $worksheetName = '') {
         //  Only read the heading row, and the configured rows
-        if (($row == 1) || ($row >= $this->_startRow && $row < $this->_endRow)) {
+        if (($row == 1) || ($row >= $this->startRow && $row < $this->endRow)) {
             return true;
         }
         return false;
diff --git a/samples/Reader/09_Simple_file_reader_using_a_read_filter.php b/samples/Reader/09_Simple_file_reader_using_a_read_filter.php
index 68100989..6e0eda14 100644
--- a/samples/Reader/09_Simple_file_reader_using_a_read_filter.php
+++ b/samples/Reader/09_Simple_file_reader_using_a_read_filter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Sample;
+namespace Samples\Sample12;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
diff --git a/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php b/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php
index e2f7c32c..b9312602 100644
--- a/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php
+++ b/samples/Reader/10_Simple_file_reader_using_a_configurable_read_filter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Sample;
+namespace Samples\Sample10;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -13,21 +13,21 @@ $sheetname = 'Data Sheet #3';
 
 class MyReadFilter implements IReadFilter
 {
-    private $_startRow = 0;
-    private $_endRow = 0;
-    private $_columns = [];
+    private $startRow = 0;
+    private $endRow = 0;
+    private $columns = [];
 
     public function __construct($startRow, $endRow, $columns)
     {
-        $this->_startRow = $startRow;
-        $this->_endRow = $endRow;
-        $this->_columns = $columns;
+        $this->startRow = $startRow;
+        $this->endRow = $endRow;
+        $this->columns = $columns;
     }
 
     public function readCell($column, $row, $worksheetName = '')
     {
-        if ($row >= $this->_startRow && $row <= $this->_endRow) {
-            if (in_array($column, $this->_columns)) {
+        if ($row >= $this->startRow && $row <= $this->endRow) {
+            if (in_array($column, $this->columns)) {
                 return true;
             }
         }
diff --git a/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php b/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php
index 19961947..a7718aaa 100644
--- a/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php
+++ b/samples/Reader/11_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_1).php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Sample;
+namespace Samples\Sample09;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -13,8 +13,8 @@ $inputFileName = __DIR__ . '/sampleData/example2.xls';
 /**  Define a Read Filter class implementing IReadFilter  */
 class ChunkReadFilter implements IReadFilter
 {
-    private $_startRow = 0;
-    private $_endRow = 0;
+    private $startRow = 0;
+    private $endRow = 0;
 
     /**
      * We expect a list of the rows that we want to read to be passed into the constructor.
@@ -24,14 +24,14 @@ class ChunkReadFilter implements IReadFilter
      */
     public function __construct($startRow, $chunkSize)
     {
-        $this->_startRow = $startRow;
-        $this->_endRow = $startRow + $chunkSize;
+        $this->startRow = $startRow;
+        $this->endRow = $startRow + $chunkSize;
     }
 
     public function readCell($column, $row, $worksheetName = '')
     {
         //  Only read the heading row, and the rows that were configured in the constructor
-        if (($row == 1) || ($row >= $this->_startRow && $row < $this->_endRow)) {
+        if (($row == 1) || ($row >= $this->startRow && $row < $this->endRow)) {
             return true;
         }
 
diff --git a/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php b/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php
index d1b85c76..c8f99af0 100644
--- a/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php
+++ b/samples/Reader/12_Reading_a_workbook_in_chunks_using_a_configurable_read_filter_(version_2).php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Sample;
+namespace Samples\Sample12;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -13,8 +13,8 @@ $inputFileName = __DIR__ . '/sampleData/example2.xls';
 /**  Define a Read Filter class implementing IReadFilter  */
 class ChunkReadFilter implements IReadFilter
 {
-    private $_startRow = 0;
-    private $_endRow = 0;
+    private $startRow = 0;
+    private $endRow = 0;
 
     /**
      * Set the list of rows that we want to read.
@@ -24,14 +24,14 @@ class ChunkReadFilter implements IReadFilter
      */
     public function setRows($startRow, $chunkSize)
     {
-        $this->_startRow = $startRow;
-        $this->_endRow = $startRow + $chunkSize;
+        $this->startRow = $startRow;
+        $this->endRow = $startRow + $chunkSize;
     }
 
     public function readCell($column, $row, $worksheetName = '')
     {
         //  Only read the heading row, and the rows that are configured in $this->_startRow and $this->_endRow
-        if (($row == 1) || ($row >= $this->_startRow && $row < $this->_endRow)) {
+        if (($row == 1) || ($row >= $this->startRow && $row < $this->endRow)) {
             return true;
         }
 
diff --git a/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php b/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php
index 80ece763..9915a097 100644
--- a/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php
+++ b/samples/Reader/14_Reading_a_large_CSV_file_in_chunks_to_split_across_multiple_worksheets.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Sample;
+namespace Samples\Sample14;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -14,8 +14,8 @@ $inputFileName = __DIR__ . '/sampleData/example2.csv';
 /**  Define a Read Filter class implementing IReadFilter  */
 class ChunkReadFilter implements IReadFilter
 {
-    private $_startRow = 0;
-    private $_endRow = 0;
+    private $startRow = 0;
+    private $endRow = 0;
 
     /**
      * Set the list of rows that we want to read.
@@ -25,14 +25,14 @@ class ChunkReadFilter implements IReadFilter
      */
     public function setRows($startRow, $chunkSize)
     {
-        $this->_startRow = $startRow;
-        $this->_endRow = $startRow + $chunkSize;
+        $this->startRow = $startRow;
+        $this->endRow = $startRow + $chunkSize;
     }
 
     public function readCell($column, $row, $worksheetName = '')
     {
         //  Only read the heading row, and the rows that are configured in $this->_startRow and $this->_endRow
-        if (($row == 1) || ($row >= $this->_startRow && $row < $this->_endRow)) {
+        if (($row == 1) || ($row >= $this->startRow && $row < $this->endRow)) {
             return true;
         }
 
diff --git a/src/PhpSpreadsheet/Cell.php b/src/PhpSpreadsheet/Cell.php
index f709310c..235ec73d 100644
--- a/src/PhpSpreadsheet/Cell.php
+++ b/src/PhpSpreadsheet/Cell.php
@@ -803,15 +803,15 @@ class Cell
         //    Using a lookup cache adds a slight memory overhead, but boosts speed
         //    caching using a static within the method is faster than a class static,
         //        though it's additional memory overhead
-        static $_indexCache = [];
+        static $indexCache = [];
 
-        if (isset($_indexCache[$pString])) {
-            return $_indexCache[$pString];
+        if (isset($indexCache[$pString])) {
+            return $indexCache[$pString];
         }
         //    It's surprising how costly the strtoupper() and ord() calls actually are, so we use a lookup array rather than use ord()
         //        and make it case insensitive to get rid of the strtoupper() as well. Because it's a static, there's no significant
         //        memory overhead either
-        static $_columnLookup = [
+        static $columnLookup = [
             'A' => 1, 'B' => 2, 'C' => 3, 'D' => 4, 'E' => 5, 'F' => 6, 'G' => 7, 'H' => 8, 'I' => 9, 'J' => 10, 'K' => 11, 'L' => 12, 'M' => 13,
             'N' => 14, 'O' => 15, 'P' => 16, 'Q' => 17, 'R' => 18, 'S' => 19, 'T' => 20, 'U' => 21, 'V' => 22, 'W' => 23, 'X' => 24, 'Y' => 25, 'Z' => 26,
             'a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5, 'f' => 6, 'g' => 7, 'h' => 8, 'i' => 9, 'j' => 10, 'k' => 11, 'l' => 12, 'm' => 13,
@@ -822,17 +822,17 @@ class Cell
         //        for improved performance
         if (isset($pString[0])) {
             if (!isset($pString[1])) {
-                $_indexCache[$pString] = $_columnLookup[$pString];
+                $indexCache[$pString] = $columnLookup[$pString];
 
-                return $_indexCache[$pString];
+                return $indexCache[$pString];
             } elseif (!isset($pString[2])) {
-                $_indexCache[$pString] = $_columnLookup[$pString[0]] * 26 + $_columnLookup[$pString[1]];
+                $indexCache[$pString] = $columnLookup[$pString[0]] * 26 + $columnLookup[$pString[1]];
 
-                return $_indexCache[$pString];
+                return $indexCache[$pString];
             } elseif (!isset($pString[3])) {
-                $_indexCache[$pString] = $_columnLookup[$pString[0]] * 676 + $_columnLookup[$pString[1]] * 26 + $_columnLookup[$pString[2]];
+                $indexCache[$pString] = $columnLookup[$pString[0]] * 676 + $columnLookup[$pString[1]] * 26 + $columnLookup[$pString[2]];
 
-                return $_indexCache[$pString];
+                return $indexCache[$pString];
             }
         }
 
diff --git a/src/PhpSpreadsheet/Reader/Xls.php b/src/PhpSpreadsheet/Reader/Xls.php
index ad302188..0ab49287 100644
--- a/src/PhpSpreadsheet/Reader/Xls.php
+++ b/src/PhpSpreadsheet/Reader/Xls.php
@@ -404,7 +404,7 @@ class Xls extends BaseReader implements IReader
     /**
      * @var string
      */
-    private $_baseCell;
+    private $baseCell;
 
     /**
      * Create a new Xls Reader instance.
@@ -3968,14 +3968,14 @@ class Xls extends BaseReader implements IReader
             // get the base cell, grab tExp token
             $baseRow = self::getUInt2d($formulaStructure, 3);
             $baseCol = self::getUInt2d($formulaStructure, 5);
-            $this->_baseCell = Cell::stringFromColumnIndex($baseCol) . ($baseRow + 1);
+            $this->baseCell = Cell::stringFromColumnIndex($baseCol) . ($baseRow + 1);
         }
 
         // Read cell?
         if (($this->getReadFilter() !== null) && $this->getReadFilter()->readCell($columnString, $row + 1, $this->phpSheet->getTitle())) {
             if ($isPartOfSharedFormula) {
                 // formula is added to this cell after the sheet has been read
-                $this->sharedFormulaParts[$columnString . ($row + 1)] = $this->_baseCell;
+                $this->sharedFormulaParts[$columnString . ($row + 1)] = $this->baseCell;
             }
 
             // offset: 16: size: 4; not used
@@ -4078,7 +4078,7 @@ class Xls extends BaseReader implements IReader
         $formula = substr($recordData, 8);
 
         // at this point we only store the shared formula for later use
-        $this->sharedFormulas[$this->_baseCell] = $formula;
+        $this->sharedFormulas[$this->baseCell] = $formula;
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php b/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
index c0102890..14f56dca 100644
--- a/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
+++ b/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
@@ -43,22 +43,22 @@ class Root extends PPS
     /**
      * @var resource
      */
-    private $_FILEH_;
+    private $fileHandle;
 
     /**
      * @var string
      */
-    private $_tmp_filename;
+    private $tempFilename;
 
     /**
      * @var int
      */
-    private $_SMALL_BLOCK_SIZE;
+    private $smallBlockSize;
 
     /**
      * @var int
      */
-    private $_BIG_BLOCK_SIZE;
+    private $bigBlockSize;
 
     /**
      * @param int $time_1st A timestamp
@@ -88,30 +88,30 @@ class Root extends PPS
     public function save($filename)
     {
         // Initial Setting for saving
-        $this->_BIG_BLOCK_SIZE = pow(
+        $this->bigBlockSize = pow(
             2,
-            (isset($this->_BIG_BLOCK_SIZE)) ? self::adjust2($this->_BIG_BLOCK_SIZE) : 9
+            (isset($this->bigBlockSize)) ? self::adjust2($this->bigBlockSize) : 9
         );
-        $this->_SMALL_BLOCK_SIZE = pow(
+        $this->smallBlockSize = pow(
             2,
-            (isset($this->_SMALL_BLOCK_SIZE)) ? self::adjust2($this->_SMALL_BLOCK_SIZE) : 6
+            (isset($this->smallBlockSize)) ? self::adjust2($this->smallBlockSize) : 6
         );
 
         if (is_resource($filename)) {
-            $this->_FILEH_ = $filename;
+            $this->fileHandle = $filename;
         } elseif ($filename == '-' || $filename == '') {
             if ($this->tempDirectory === null) {
                 $this->tempDirectory = \PhpOffice\PhpSpreadsheet\Shared\File::sysGetTempDir();
             }
-            $this->_tmp_filename = tempnam($this->tempDirectory, 'OLE_PPS_Root');
-            $this->_FILEH_ = fopen($this->_tmp_filename, 'w+b');
-            if ($this->_FILEH_ == false) {
+            $this->tempFilename = tempnam($this->tempDirectory, 'OLE_PPS_Root');
+            $this->fileHandle = fopen($this->tempFilename, 'w+b');
+            if ($this->fileHandle == false) {
                 throw new WriterException("Can't create temporary file.");
             }
         } else {
-            $this->_FILEH_ = fopen($filename, 'wb');
+            $this->fileHandle = fopen($filename, 'wb');
         }
-        if ($this->_FILEH_ == false) {
+        if ($this->fileHandle == false) {
             throw new WriterException("Can't open $filename. It may be in use or protected.");
         }
         // Make an array of PPS's (for Save)
@@ -133,7 +133,7 @@ class Root extends PPS
         $this->_saveBbd($iSBDcnt, $iBBcnt, $iPPScnt);
 
         if (!is_resource($filename)) {
-            fclose($this->_FILEH_);
+            fclose($this->fileHandle);
         }
 
         return true;
@@ -157,21 +157,21 @@ class Root extends PPS
             if ($raList[$i]->Type == OLE::OLE_PPS_TYPE_FILE) {
                 $raList[$i]->Size = $raList[$i]->getDataLen();
                 if ($raList[$i]->Size < OLE::OLE_DATA_SIZE_SMALL) {
-                    $iSBcnt += floor($raList[$i]->Size / $this->_SMALL_BLOCK_SIZE)
-                                  + (($raList[$i]->Size % $this->_SMALL_BLOCK_SIZE) ? 1 : 0);
+                    $iSBcnt += floor($raList[$i]->Size / $this->smallBlockSize)
+                                  + (($raList[$i]->Size % $this->smallBlockSize) ? 1 : 0);
                 } else {
-                    $iBBcnt += (floor($raList[$i]->Size / $this->_BIG_BLOCK_SIZE) +
-                        (($raList[$i]->Size % $this->_BIG_BLOCK_SIZE) ? 1 : 0));
+                    $iBBcnt += (floor($raList[$i]->Size / $this->bigBlockSize) +
+                        (($raList[$i]->Size % $this->bigBlockSize) ? 1 : 0));
                 }
             }
         }
-        $iSmallLen = $iSBcnt * $this->_SMALL_BLOCK_SIZE;
-        $iSlCnt = floor($this->_BIG_BLOCK_SIZE / OLE::OLE_LONG_INT_SIZE);
+        $iSmallLen = $iSBcnt * $this->smallBlockSize;
+        $iSlCnt = floor($this->bigBlockSize / OLE::OLE_LONG_INT_SIZE);
         $iSBDcnt = floor($iSBcnt / $iSlCnt) + (($iSBcnt % $iSlCnt) ? 1 : 0);
-        $iBBcnt += (floor($iSmallLen / $this->_BIG_BLOCK_SIZE) +
-                      (($iSmallLen % $this->_BIG_BLOCK_SIZE) ? 1 : 0));
+        $iBBcnt += (floor($iSmallLen / $this->bigBlockSize) +
+                      (($iSmallLen % $this->bigBlockSize) ? 1 : 0));
         $iCnt = count($raList);
-        $iBdCnt = $this->_BIG_BLOCK_SIZE / OLE::OLE_PPS_SIZE;
+        $iBdCnt = $this->bigBlockSize / OLE::OLE_PPS_SIZE;
         $iPPScnt = (floor($iCnt / $iBdCnt) + (($iCnt % $iBdCnt) ? 1 : 0));
 
         return [$iSBDcnt, $iBBcnt, $iPPScnt];
@@ -202,11 +202,11 @@ class Root extends PPS
      */
     public function _saveHeader($iSBDcnt, $iBBcnt, $iPPScnt)
     {
-        $FILE = $this->_FILEH_;
+        $FILE = $this->fileHandle;
 
         // Calculate Basic Setting
-        $iBlCnt = $this->_BIG_BLOCK_SIZE / OLE::OLE_LONG_INT_SIZE;
-        $i1stBdL = ($this->_BIG_BLOCK_SIZE - 0x4C) / OLE::OLE_LONG_INT_SIZE;
+        $iBlCnt = $this->bigBlockSize / OLE::OLE_LONG_INT_SIZE;
+        $i1stBdL = ($this->bigBlockSize - 0x4C) / OLE::OLE_LONG_INT_SIZE;
 
         $iBdExL = 0;
         $iAll = $iBBcnt + $iPPScnt + $iSBDcnt;
@@ -281,7 +281,7 @@ class Root extends PPS
      */
     public function _saveBigData($iStBlk, &$raList)
     {
-        $FILE = $this->_FILEH_;
+        $FILE = $this->fileHandle;
 
         // cycle through PPS's
         $iCount = count($raList);
@@ -291,14 +291,14 @@ class Root extends PPS
                 if (($raList[$i]->Size >= OLE::OLE_DATA_SIZE_SMALL) || (($raList[$i]->Type == OLE::OLE_PPS_TYPE_ROOT) && isset($raList[$i]->_data))) {
                     fwrite($FILE, $raList[$i]->_data);
 
-                    if ($raList[$i]->Size % $this->_BIG_BLOCK_SIZE) {
-                        fwrite($FILE, str_repeat("\x00", $this->_BIG_BLOCK_SIZE - ($raList[$i]->Size % $this->_BIG_BLOCK_SIZE)));
+                    if ($raList[$i]->Size % $this->bigBlockSize) {
+                        fwrite($FILE, str_repeat("\x00", $this->bigBlockSize - ($raList[$i]->Size % $this->bigBlockSize)));
                     }
                     // Set For PPS
                     $raList[$i]->startBlock = $iStBlk;
                     $iStBlk +=
-                            (floor($raList[$i]->Size / $this->_BIG_BLOCK_SIZE) +
-                                (($raList[$i]->Size % $this->_BIG_BLOCK_SIZE) ? 1 : 0));
+                            (floor($raList[$i]->Size / $this->bigBlockSize) +
+                                (($raList[$i]->Size % $this->bigBlockSize) ? 1 : 0));
                 }
             }
         }
@@ -312,7 +312,7 @@ class Root extends PPS
     public function _makeSmallData(&$raList)
     {
         $sRes = '';
-        $FILE = $this->_FILEH_;
+        $FILE = $this->fileHandle;
         $iSmBlk = 0;
 
         $iCount = count($raList);
@@ -323,8 +323,8 @@ class Root extends PPS
                     continue;
                 }
                 if ($raList[$i]->Size < OLE::OLE_DATA_SIZE_SMALL) {
-                    $iSmbCnt = floor($raList[$i]->Size / $this->_SMALL_BLOCK_SIZE)
-                                  + (($raList[$i]->Size % $this->_SMALL_BLOCK_SIZE) ? 1 : 0);
+                    $iSmbCnt = floor($raList[$i]->Size / $this->smallBlockSize)
+                                  + (($raList[$i]->Size % $this->smallBlockSize) ? 1 : 0);
                     // Add to SBD
                     $jB = $iSmbCnt - 1;
                     for ($j = 0; $j < $jB; ++$j) {
@@ -334,8 +334,8 @@ class Root extends PPS
 
                     // Add to Data String(this will be written for RootEntry)
                     $sRes .= $raList[$i]->_data;
-                    if ($raList[$i]->Size % $this->_SMALL_BLOCK_SIZE) {
-                        $sRes .= str_repeat("\x00", $this->_SMALL_BLOCK_SIZE - ($raList[$i]->Size % $this->_SMALL_BLOCK_SIZE));
+                    if ($raList[$i]->Size % $this->smallBlockSize) {
+                        $sRes .= str_repeat("\x00", $this->smallBlockSize - ($raList[$i]->Size % $this->smallBlockSize));
                     }
                     // Set for PPS
                     $raList[$i]->startBlock = $iSmBlk;
@@ -343,7 +343,7 @@ class Root extends PPS
                 }
             }
         }
-        $iSbCnt = floor($this->_BIG_BLOCK_SIZE / OLE::OLE_LONG_INT_SIZE);
+        $iSbCnt = floor($this->bigBlockSize / OLE::OLE_LONG_INT_SIZE);
         if ($iSmBlk % $iSbCnt) {
             $iB = $iSbCnt - ($iSmBlk % $iSbCnt);
             for ($i = 0; $i < $iB; ++$i) {
@@ -364,13 +364,13 @@ class Root extends PPS
         // Save each PPS WK
         $iC = count($raList);
         for ($i = 0; $i < $iC; ++$i) {
-            fwrite($this->_FILEH_, $raList[$i]->_getPpsWk());
+            fwrite($this->fileHandle, $raList[$i]->_getPpsWk());
         }
         // Adjust for Block
         $iCnt = count($raList);
-        $iBCnt = $this->_BIG_BLOCK_SIZE / OLE::OLE_PPS_SIZE;
+        $iBCnt = $this->bigBlockSize / OLE::OLE_PPS_SIZE;
         if ($iCnt % $iBCnt) {
-            fwrite($this->_FILEH_, str_repeat("\x00", ($iBCnt - ($iCnt % $iBCnt)) * OLE::OLE_PPS_SIZE));
+            fwrite($this->fileHandle, str_repeat("\x00", ($iBCnt - ($iCnt % $iBCnt)) * OLE::OLE_PPS_SIZE));
         }
     }
 
@@ -383,10 +383,10 @@ class Root extends PPS
      */
     public function _saveBbd($iSbdSize, $iBsize, $iPpsCnt)
     {
-        $FILE = $this->_FILEH_;
+        $FILE = $this->fileHandle;
         // Calculate Basic Setting
-        $iBbCnt = $this->_BIG_BLOCK_SIZE / OLE::OLE_LONG_INT_SIZE;
-        $i1stBdL = ($this->_BIG_BLOCK_SIZE - 0x4C) / OLE::OLE_LONG_INT_SIZE;
+        $iBbCnt = $this->bigBlockSize / OLE::OLE_LONG_INT_SIZE;
+        $i1stBdL = ($this->bigBlockSize - 0x4C) / OLE::OLE_LONG_INT_SIZE;
 
         $iBdExL = 0;
         $iAll = $iBsize + $iPpsCnt + $iSbdSize;
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
index 11a74e5d..175059f9 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
@@ -21,7 +21,7 @@ class Chart extends WriterPart
     /**
      * @var int
      */
-    private $_seriesIndex;
+    private $seriesIndex;
 
     /**
      * Write charts to XML format.
@@ -220,7 +220,7 @@ class Chart extends WriterPart
         }
 
         $id1 = $id2 = 0;
-        $this->_seriesIndex = 0;
+        $this->seriesIndex = 0;
         $objWriter->startElement('c:plotArea');
 
         $layout = $plotArea->getLayout();
@@ -1096,11 +1096,11 @@ class Chart extends WriterPart
             }
 
             $objWriter->startElement('c:idx');
-            $objWriter->writeAttribute('val', $this->_seriesIndex + $plotSeriesIdx);
+            $objWriter->writeAttribute('val', $this->seriesIndex + $plotSeriesIdx);
             $objWriter->endElement();
 
             $objWriter->startElement('c:order');
-            $objWriter->writeAttribute('val', $this->_seriesIndex + $plotSeriesRef);
+            $objWriter->writeAttribute('val', $this->seriesIndex + $plotSeriesRef);
             $objWriter->endElement();
 
             if (($groupType == DataSeries::TYPE_PIECHART) || ($groupType == DataSeries::TYPE_PIECHART_3D) || ($groupType == DataSeries::TYPE_DONUTCHART)) {
@@ -1218,7 +1218,7 @@ class Chart extends WriterPart
             $objWriter->endElement();
         }
 
-        $this->_seriesIndex += $plotSeriesIdx + 1;
+        $this->seriesIndex += $plotSeriesIdx + 1;
     }
 
     /**
diff --git a/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php b/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php
index 9543a543..112d4336 100644
--- a/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php
+++ b/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php
@@ -4,7 +4,7 @@ namespace PhpOffice\PhpSpreadsheetTests\Custom;
 
 class ComplexAssert
 {
-    private $_errorMessage = '';
+    private $errorMessage = '';
 
     public function assertComplexEquals($expected, $actual, $delta = 0)
     {
@@ -13,7 +13,7 @@ class ComplexAssert
             if ($expected === $actual) {
                 return true;
             }
-            $this->_errorMessage = 'Expected Error: ' . $actual . ' !== ' . $expected;
+            $this->errorMessage = 'Expected Error: ' . $actual . ' !== ' . $expected;
 
             return false;
         }
@@ -23,7 +23,7 @@ class ComplexAssert
 
         if (!is_numeric($actualComplex->getReal()) || !is_numeric($expectedComplex->getReal())) {
             if ($actualComplex->getReal() !== $expectedComplex->getReal()) {
-                $this->_errorMessage = 'Mismatched String: ' . $actualComplex->getReal() . ' !== ' . $expectedComplex->getReal();
+                $this->errorMessage = 'Mismatched String: ' . $actualComplex->getReal() . ' !== ' . $expectedComplex->getReal();
 
                 return false;
             }
@@ -33,20 +33,20 @@ class ComplexAssert
 
         if ($actualComplex->getReal() < ($expectedComplex->getReal() - $delta) ||
             $actualComplex->getReal() > ($expectedComplex->getReal() + $delta)) {
-            $this->_errorMessage = 'Mismatched Real part: ' . $actualComplex->getReal() . ' != ' . $expectedComplex->getReal();
+            $this->errorMessage = 'Mismatched Real part: ' . $actualComplex->getReal() . ' != ' . $expectedComplex->getReal();
 
             return false;
         }
 
         if ($actualComplex->getImaginary() < ($expectedComplex->getImaginary() - $delta) ||
             $actualComplex->getImaginary() > ($expectedComplex->getImaginary() + $delta)) {
-            $this->_errorMessage = 'Mismatched Imaginary part: ' . $actualComplex->getImaginary() . ' != ' . $expectedComplex->getImaginary();
+            $this->errorMessage = 'Mismatched Imaginary part: ' . $actualComplex->getImaginary() . ' != ' . $expectedComplex->getImaginary();
 
             return false;
         }
 
         if ($actualComplex->getSuffix() !== $actualComplex->getSuffix()) {
-            $this->_errorMessage = 'Mismatched Suffix: ' . $actualComplex->getSuffix() . ' != ' . $expectedComplex->getSuffix();
+            $this->errorMessage = 'Mismatched Suffix: ' . $actualComplex->getSuffix() . ' != ' . $expectedComplex->getSuffix();
 
             return false;
         }
@@ -56,6 +56,6 @@ class ComplexAssert
 
     public function getErrorMessage()
     {
-        return $this->_errorMessage;
+        return $this->errorMessage;
     }
 }