diff --git a/src/Spout/Common/Escaper/ODS.php b/src/Spout/Common/Escaper/ODS.php
index 3e252a7..86caeb3 100644
--- a/src/Spout/Common/Escaper/ODS.php
+++ b/src/Spout/Common/Escaper/ODS.php
@@ -2,6 +2,8 @@
 
 namespace Box\Spout\Common\Escaper;
 
+use Box\Spout\Common\Singleton;
+
 /**
  * Class ODS
  * Provides functions to escape and unescape data for ODS files
@@ -10,6 +12,8 @@ namespace Box\Spout\Common\Escaper;
  */
 class ODS implements EscaperInterface
 {
+    use Singleton;
+
     /**
      * Escapes the given string to make it compatible with XLSX
      *
diff --git a/src/Spout/Common/Escaper/XLSX.php b/src/Spout/Common/Escaper/XLSX.php
index 6f5bd1f..b5719a0 100644
--- a/src/Spout/Common/Escaper/XLSX.php
+++ b/src/Spout/Common/Escaper/XLSX.php
@@ -2,6 +2,8 @@
 
 namespace Box\Spout\Common\Escaper;
 
+use Box\Spout\Common\Singleton;
+
 /**
  * Class XLSX
  * Provides functions to escape and unescape data for XLSX files
@@ -10,13 +12,15 @@ namespace Box\Spout\Common\Escaper;
  */
 class XLSX implements EscaperInterface
 {
+    use Singleton;
+
     /** @var string[] Control characters to be escaped */
     protected $controlCharactersEscapingMap;
 
     /**
-     *
+     * Initializes the singleton instance
      */
-    public function __construct()
+    protected function init()
     {
         $this->controlCharactersEscapingMap = $this->getControlCharactersEscapingMap();
     }
diff --git a/src/Spout/Common/Helper/EncodingHelper.php b/src/Spout/Common/Helper/EncodingHelper.php
index 3edd7a1..3a30aaa 100644
--- a/src/Spout/Common/Helper/EncodingHelper.php
+++ b/src/Spout/Common/Helper/EncodingHelper.php
@@ -59,7 +59,7 @@ class EncodingHelper
     {
         $byteOffsetToSkipBom = 0;
 
-        if ($this->hasBom($filePointer, $encoding)) {
+        if ($this->hasBOM($filePointer, $encoding)) {
             $bomUsed = $this->supportedEncodingsWithBom[$encoding];
 
             // we skip the N first bytes
diff --git a/src/Spout/Common/Singleton.php b/src/Spout/Common/Singleton.php
new file mode 100644
index 0000000..015ede8
--- /dev/null
+++ b/src/Spout/Common/Singleton.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace Box\Spout\Common;
+
+/**
+ * Class Singleton
+ * Defines a class as a singleton.
+ *
+ * @package Box\Spout\Common
+ */
+trait Singleton
+{
+    protected static $instance;
+
+    /**
+     * @return static
+     */
+    final public static function getInstance()
+    {
+        return isset(static::$instance)
+            ? static::$instance
+            : static::$instance = new static;
+    }
+
+    /**
+     * Singleton constructor.
+     */
+    final private function __construct()
+    {
+        $this->init();
+    }
+
+    /**
+     * Initializes the singleton
+     * @return void
+     */
+    protected function init() {}
+
+    final private function __wakeup() {}
+    final private function __clone() {}
+}
diff --git a/src/Spout/Reader/CSV/RowIterator.php b/src/Spout/Reader/CSV/RowIterator.php
index 95b2596..5189dfc 100644
--- a/src/Spout/Reader/CSV/RowIterator.php
+++ b/src/Spout/Reader/CSV/RowIterator.php
@@ -57,6 +57,7 @@ class RowIterator implements IteratorInterface
      * @param string $fieldDelimiter Character that delimits fields
      * @param string $fieldEnclosure Character that enclose fields
      * @param string $encoding Encoding of the CSV file to be read
+     * @param string $endOfLineDelimiter End of line delimiter
      * @param \Box\Spout\Common\Helper\GlobalFunctionsHelper $globalFunctionsHelper
      */
     public function __construct($filePointer, $fieldDelimiter, $fieldEnclosure, $encoding, $endOfLineDelimiter, $globalFunctionsHelper)
diff --git a/src/Spout/Reader/ODS/Helper/CellValueFormatter.php b/src/Spout/Reader/ODS/Helper/CellValueFormatter.php
index b39af21..38c1c85 100644
--- a/src/Spout/Reader/ODS/Helper/CellValueFormatter.php
+++ b/src/Spout/Reader/ODS/Helper/CellValueFormatter.php
@@ -48,7 +48,7 @@ class CellValueFormatter
         $this->shouldFormatDates = $shouldFormatDates;
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $this->escaper = new \Box\Spout\Common\Escaper\ODS();
+        $this->escaper = \Box\Spout\Common\Escaper\ODS::getInstance();
     }
 
     /**
diff --git a/src/Spout/Reader/ODS/SheetIterator.php b/src/Spout/Reader/ODS/SheetIterator.php
index d0010bd..f6cfdbe 100644
--- a/src/Spout/Reader/ODS/SheetIterator.php
+++ b/src/Spout/Reader/ODS/SheetIterator.php
@@ -15,6 +15,8 @@ use Box\Spout\Reader\Wrapper\XMLReader;
  */
 class SheetIterator implements IteratorInterface
 {
+    const CONTENT_XML_FILE_PATH = 'content.xml';
+
     /** Definition of XML nodes name and attribute used to parse sheet data */
     const XML_NODE_TABLE = 'table:table';
     const XML_ATTRIBUTE_TABLE_NAME = 'table:name';
@@ -49,7 +51,7 @@ class SheetIterator implements IteratorInterface
         $this->xmlReader = new XMLReader();
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $this->escaper = new \Box\Spout\Common\Escaper\ODS();
+        $this->escaper = \Box\Spout\Common\Escaper\ODS::getInstance();
     }
 
     /**
@@ -63,8 +65,8 @@ class SheetIterator implements IteratorInterface
     {
         $this->xmlReader->close();
 
-        $contentXmlFilePath = $this->filePath . '#content.xml';
-        if ($this->xmlReader->open('zip://' . $contentXmlFilePath) === false) {
+        if ($this->xmlReader->openFileInZip($this->filePath, self::CONTENT_XML_FILE_PATH) === false) {
+            $contentXmlFilePath = $this->filePath . '#' . self::CONTENT_XML_FILE_PATH;
             throw new IOException("Could not open \"{$contentXmlFilePath}\".");
         }
 
diff --git a/src/Spout/Reader/Wrapper/XMLReader.php b/src/Spout/Reader/Wrapper/XMLReader.php
index 42bd92c..c979819 100644
--- a/src/Spout/Reader/Wrapper/XMLReader.php
+++ b/src/Spout/Reader/Wrapper/XMLReader.php
@@ -14,66 +14,44 @@ class XMLReader extends \XMLReader
 {
     use XMLInternalErrorsHelper;
 
+    const ZIP_WRAPPER = 'zip://';
+
     /**
-     * Set the URI containing the XML to parse
-     * @see \XMLReader::open
+     * Opens the XML Reader to read a file located inside a ZIP file.
      *
-     * @param string $URI URI pointing to the document
-   	 * @param string|null|void $encoding The document encoding
-   	 * @param int $options A bitmask of the LIBXML_* constants
+     * @param string $zipFilePath Path to the ZIP file
+     * @param string $fileInsideZipPath Relative or absolute path of the file inside the zip
      * @return bool TRUE on success or FALSE on failure
      */
-    public function open($URI, $encoding = null, $options = 0)
+    public function openFileInZip($zipFilePath, $fileInsideZipPath)
     {
         $wasOpenSuccessful = false;
-        $realPathURI = $this->convertURIToUseRealPath($URI);
+        $realPathURI = $this->getRealPathURIForFileInZip($zipFilePath, $fileInsideZipPath);
 
         // HHVM does not check if file exists within zip file
         // @link https://github.com/facebook/hhvm/issues/5779
-        if ($this->isRunningHHVM() && $this->isZipStream($realPathURI)) {
+        if ($this->isRunningHHVM()) {
             if ($this->fileExistsWithinZip($realPathURI)) {
-                $wasOpenSuccessful = parent::open($realPathURI, $encoding, $options|LIBXML_NONET);
+                $wasOpenSuccessful = $this->open($realPathURI, null, LIBXML_NONET);
             }
         } else {
-            $wasOpenSuccessful = parent::open($realPathURI, $encoding, $options|LIBXML_NONET);
+            $wasOpenSuccessful = $this->open($realPathURI, null, LIBXML_NONET);
         }
 
         return $wasOpenSuccessful;
     }
 
     /**
-     * Updates the given URI to use a real path.
-     * This is to avoid issues on some Windows setup.
+     * Returns the real path for the given path components.
+     * This is useful to avoid issues on some Windows setup.
      *
-     * @param string $URI URI
-     * @return string The URI using a real path
+     * @param string $zipFilePath Path to the ZIP file
+     * @param string $fileInsideZipPath Relative or absolute path of the file inside the zip
+     * @return string The real path URI
      */
-    protected function convertURIToUseRealPath($URI)
+    public function getRealPathURIForFileInZip($zipFilePath, $fileInsideZipPath)
     {
-        $realPathURI = $URI;
-
-        if ($this->isZipStream($URI)) {
-            if (preg_match('/zip:\/\/(.*)#(.*)/', $URI, $matches)) {
-                $documentPath = $matches[1];
-                $documentInsideZipPath = $matches[2];
-                $realPathURI = 'zip://' . realpath($documentPath) . '#' . $documentInsideZipPath;
-            }
-        } else {
-            $realPathURI = realpath($URI);
-        }
-
-        return $realPathURI;
-    }
-
-    /**
-     * Returns whether the given URI is a zip stream.
-     *
-     * @param string $URI URI pointing to a document
-     * @return bool TRUE if URI is a zip stream, FALSE otherwise
-     */
-    protected function isZipStream($URI)
-    {
-        return (strpos($URI, 'zip://') === 0);
+        return (self::ZIP_WRAPPER . realpath($zipFilePath) . '#' . $fileInsideZipPath);
     }
 
     /**
@@ -138,9 +116,10 @@ class XMLReader extends \XMLReader
      */
     public function readUntilNodeFound($nodeName)
     {
-        while (($wasReadSuccessful = $this->read()) && ($this->nodeType !== \XMLReader::ELEMENT || $this->name !== $nodeName)) {
-            // do nothing
-        }
+        do {
+            $wasReadSuccessful = $this->read();
+            $isNotPositionedOnStartingNode = !$this->isPositionedOnStartingNode($nodeName);
+        } while ($wasReadSuccessful && $isNotPositionedOnStartingNode);
 
         return $wasReadSuccessful;
     }
@@ -170,7 +149,7 @@ class XMLReader extends \XMLReader
      */
     public function isPositionedOnStartingNode($nodeName)
     {
-        return ($this->nodeType === XMLReader::ELEMENT && $this->name === $nodeName);
+        return $this->isPositionedOnNode($nodeName, XMLReader::ELEMENT);
     }
 
     /**
@@ -179,6 +158,22 @@ class XMLReader extends \XMLReader
      */
     public function isPositionedOnEndingNode($nodeName)
     {
-        return ($this->nodeType === XMLReader::END_ELEMENT && $this->name === $nodeName);
+        return $this->isPositionedOnNode($nodeName, XMLReader::END_ELEMENT);
+    }
+
+    /**
+     * @param string $nodeName
+     * @param int $nodeType
+     * @return bool Whether the XML Reader is currently positioned on the node with given name and type
+     */
+    private function isPositionedOnNode($nodeName, $nodeType)
+    {
+        // In some cases, the node has a prefix (for instance, "<sheet>" can also be "<x:sheet>").
+        // So if the given node name does not have a prefix, we need to look at the unprefixed name ("localName").
+        // @see https://github.com/box/spout/issues/233
+        $hasPrefix = (strpos($nodeName, ':') !== false);
+        $currentNodeName = ($hasPrefix) ? $this->name : $this->localName;
+
+        return ($this->nodeType === $nodeType && $currentNodeName === $nodeName);
     }
 }
diff --git a/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php b/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php
index 286d348..a272a2e 100644
--- a/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php
+++ b/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php
@@ -62,7 +62,7 @@ class CellValueFormatter
         $this->shouldFormatDates = $shouldFormatDates;
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $this->escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $this->escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
     }
 
     /**
diff --git a/src/Spout/Reader/XLSX/Helper/SharedStringsHelper.php b/src/Spout/Reader/XLSX/Helper/SharedStringsHelper.php
index 1ba4e6a..750c53e 100644
--- a/src/Spout/Reader/XLSX/Helper/SharedStringsHelper.php
+++ b/src/Spout/Reader/XLSX/Helper/SharedStringsHelper.php
@@ -80,7 +80,7 @@ class SharedStringsHelper
         $xmlReader = new XMLReader();
         $sharedStringIndex = 0;
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
 
         $sharedStringsFilePath = $this->getSharedStringsFilePath();
         if ($xmlReader->open($sharedStringsFilePath) === false) {
diff --git a/src/Spout/Reader/XLSX/Helper/SheetHelper.php b/src/Spout/Reader/XLSX/Helper/SheetHelper.php
index 5f74f44..a6ff909 100644
--- a/src/Spout/Reader/XLSX/Helper/SheetHelper.php
+++ b/src/Spout/Reader/XLSX/Helper/SheetHelper.php
@@ -2,7 +2,7 @@
 
 namespace Box\Spout\Reader\XLSX\Helper;
 
-use Box\Spout\Reader\Wrapper\SimpleXMLElement;
+use Box\Spout\Reader\Wrapper\XMLReader;
 use Box\Spout\Reader\XLSX\Sheet;
 
 /**
@@ -17,10 +17,6 @@ class SheetHelper
     const WORKBOOK_XML_RELS_FILE_PATH = 'xl/_rels/workbook.xml.rels';
     const WORKBOOK_XML_FILE_PATH = 'xl/workbook.xml';
 
-    /** Namespaces for the XML files */
-    const MAIN_NAMESPACE_FOR_WORKBOOK_XML_RELS = 'http://schemas.openxmlformats.org/package/2006/relationships';
-    const MAIN_NAMESPACE_FOR_WORKBOOK_XML = 'http://schemas.openxmlformats.org/spreadsheetml/2006/main';
-
     /** @var string Path of the XLSX file being read */
     protected $filePath;
 
@@ -33,12 +29,6 @@ class SheetHelper
     /** @var bool Whether date/time values should be returned as PHP objects or be formatted as strings */
     protected $shouldFormatDates;
 
-    /** @var \Box\Spout\Reader\Wrapper\SimpleXMLElement XML element representing the workbook.xml.rels file */
-    protected $workbookXMLRelsAsXMLElement;
-
-    /** @var \Box\Spout\Reader\Wrapper\SimpleXMLElement XML element representing the workbook.xml file */
-    protected $workbookXMLAsXMLElement;
-
     /**
      * @param string $filePath Path of the XLSX file being read
      * @param \Box\Spout\Reader\XLSX\Helper\SharedStringsHelper Helper to work with shared strings
@@ -62,13 +52,21 @@ class SheetHelper
     public function getSheets()
     {
         $sheets = [];
+        $sheetIndex = 0;
 
-        // Starting from "workbook.xml" as this file is the source of truth for the sheets order
-        $workbookXMLElement = $this->getWorkbookXMLAsXMLElement();
-        $sheetNodes = $workbookXMLElement->xpath('//ns:sheet');
+        $xmlReader = new XMLReader();
+        if ($xmlReader->openFileInZip($this->filePath, self::WORKBOOK_XML_FILE_PATH)) {
+            while ($xmlReader->read()) {
+                if ($xmlReader->isPositionedOnStartingNode('sheet')) {
+                    $sheets[] = $this->getSheetFromSheetXMLNode($xmlReader, $sheetIndex);
+                    $sheetIndex++;
+                } else if ($xmlReader->isPositionedOnEndingNode('sheets')) {
+                    // stop reading once all sheets have been read
+                    break;
+                }
+            }
 
-        foreach ($sheetNodes as $sheetIndex => $sheetNode) {
-            $sheets[] = $this->getSheetFromSheetXMLNode($sheetNode, $sheetIndex);
+            $xmlReader->close();
         }
 
         return $sheets;
@@ -79,88 +77,56 @@ class SheetHelper
      * We can find the XML file path describing the sheet inside "workbook.xml.res", by mapping with the sheet ID
      * ("r:id" in "workbook.xml", "Id" in "workbook.xml.res").
      *
-     * @param \Box\Spout\Reader\Wrapper\SimpleXMLElement $sheetNode XML Node describing the sheet, as defined in "workbook.xml"
+     * @param \Box\Spout\Reader\Wrapper\XMLReader $xmlReaderOnSheetNode XML Reader instance, pointing on the node describing the sheet, as defined in "workbook.xml"
      * @param int $sheetIndexZeroBased Index of the sheet, based on order of appearance in the workbook (zero-based)
      * @return \Box\Spout\Reader\XLSX\Sheet Sheet instance
      */
-    protected function getSheetFromSheetXMLNode($sheetNode, $sheetIndexZeroBased)
+    protected function getSheetFromSheetXMLNode($xmlReaderOnSheetNode, $sheetIndexZeroBased)
     {
-        // To retrieve namespaced attributes, some versions of LibXML will accept prefixing the attribute
-        // with the namespace directly (tested on LibXML 2.9.3). For older versions (tested on LibXML 2.7.8),
-        // attributes need to be retrieved without the namespace hint.
-        $sheetId = $sheetNode->getAttribute('r:id');
-        if ($sheetId === null) {
-            $sheetId = $sheetNode->getAttribute('id');
-        }
-
-        $escapedSheetName = $sheetNode->getAttribute('name');
+        $sheetId = $xmlReaderOnSheetNode->getAttribute('r:id');
+        $escapedSheetName = $xmlReaderOnSheetNode->getAttribute('name');
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
         $sheetName = $escaper->unescape($escapedSheetName);
 
-        // find the file path of the sheet, by looking at the "workbook.xml.res" file
-        $workbookXMLResElement = $this->getWorkbookXMLRelsAsXMLElement();
-        $relationshipNodes = $workbookXMLResElement->xpath('//ns:Relationship[@Id="' . $sheetId . '"]');
-        $relationshipNode = $relationshipNodes[0];
-
-        // In workbook.xml.rels, it is only "worksheets/sheet1.xml"
-        // In [Content_Types].xml, the path is "/xl/worksheets/sheet1.xml"
-        $sheetDataXMLFilePath = '/xl/' . $relationshipNode->getAttribute('Target');
+        $sheetDataXMLFilePath = $this->getSheetDataXMLFilePathForSheetId($sheetId);
 
         return new Sheet($this->filePath, $sheetDataXMLFilePath, $this->sharedStringsHelper, $this->shouldFormatDates, $sheetIndexZeroBased, $sheetName);
     }
 
     /**
-     * Returns a representation of the workbook.xml.rels file, ready to be parsed.
-     * The returned value is cached.
-     *
-     * @return \Box\Spout\Reader\Wrapper\SimpleXMLElement XML element representating the workbook.xml.rels file
+     * @param string $sheetId The sheet ID, as defined in "workbook.xml"
+     * @return string The XML file path describing the sheet inside "workbook.xml.res", for the given sheet ID
      */
-    protected function getWorkbookXMLRelsAsXMLElement()
+    protected function getSheetDataXMLFilePathForSheetId($sheetId)
     {
-        if (!$this->workbookXMLRelsAsXMLElement) {
-            $this->workbookXMLRelsAsXMLElement = $this->getFileAsXMLElementWithNamespace(
-                self::WORKBOOK_XML_RELS_FILE_PATH,
-                self::MAIN_NAMESPACE_FOR_WORKBOOK_XML_RELS
-            );
+        $sheetDataXMLFilePath = '';
+
+        // find the file path of the sheet, by looking at the "workbook.xml.res" file
+        $xmlReader = new XMLReader();
+        if ($xmlReader->openFileInZip($this->filePath, self::WORKBOOK_XML_RELS_FILE_PATH)) {
+            while ($xmlReader->read()) {
+                if ($xmlReader->isPositionedOnStartingNode('Relationship')) {
+                    $relationshipSheetId = $xmlReader->getAttribute('Id');
+
+                    if ($relationshipSheetId === $sheetId) {
+                        // In workbook.xml.rels, it is only "worksheets/sheet1.xml"
+                        // In [Content_Types].xml, the path is "/xl/worksheets/sheet1.xml"
+                        $sheetDataXMLFilePath = $xmlReader->getAttribute('Target');
+
+                        // sometimes, the sheet data file path already contains "/xl/"...
+                        if (strpos($sheetDataXMLFilePath, '/xl/') !== 0) {
+                            $sheetDataXMLFilePath = '/xl/' . $sheetDataXMLFilePath;
+                            break;
+                        }
+                    }
+                }
+            }
+
+            $xmlReader->close();
         }
 
-        return $this->workbookXMLRelsAsXMLElement;
-    }
-
-    /**
-     * Returns a representation of the workbook.xml file, ready to be parsed.
-     * The returned value is cached.
-     *
-     * @return \Box\Spout\Reader\Wrapper\SimpleXMLElement XML element representating the workbook.xml.rels file
-     */
-    protected function getWorkbookXMLAsXMLElement()
-    {
-        if (!$this->workbookXMLAsXMLElement) {
-            $this->workbookXMLAsXMLElement = $this->getFileAsXMLElementWithNamespace(
-                self::WORKBOOK_XML_FILE_PATH,
-                self::MAIN_NAMESPACE_FOR_WORKBOOK_XML
-            );
-        }
-
-        return $this->workbookXMLAsXMLElement;
-    }
-
-    /**
-     * Loads the contents of the given file in an XML parser and register the given XPath namespace.
-     *
-     * @param string $xmlFilePath The path of the XML file inside the XLSX file
-     * @param string $mainNamespace The main XPath namespace to register
-     * @return \Box\Spout\Reader\Wrapper\SimpleXMLElement The XML element representing the file
-     */
-    protected function getFileAsXMLElementWithNamespace($xmlFilePath, $mainNamespace)
-    {
-        $xmlContents = $this->globalFunctionsHelper->file_get_contents('zip://' . $this->filePath . '#' . $xmlFilePath);
-
-        $xmlElement = new SimpleXMLElement($xmlContents);
-        $xmlElement->registerXPathNamespace('ns', $mainNamespace);
-
-        return $xmlElement;
+        return $sheetDataXMLFilePath;
     }
 }
diff --git a/src/Spout/Reader/XLSX/Helper/StyleHelper.php b/src/Spout/Reader/XLSX/Helper/StyleHelper.php
index 462433c..6fdcd80 100644
--- a/src/Spout/Reader/XLSX/Helper/StyleHelper.php
+++ b/src/Spout/Reader/XLSX/Helper/StyleHelper.php
@@ -76,10 +76,9 @@ class StyleHelper
         $this->customNumberFormats = [];
         $this->stylesAttributes = [];
 
-        $stylesXmlFilePath = $this->filePath .'#' . self::STYLES_XML_FILE_PATH;
         $xmlReader = new XMLReader();
 
-        if ($xmlReader->open('zip://' . $stylesXmlFilePath)) {
+        if ($xmlReader->openFileInZip($this->filePath, self::STYLES_XML_FILE_PATH)) {
             while ($xmlReader->read()) {
                 if ($xmlReader->isPositionedOnStartingNode(self::XML_NODE_NUM_FMTS)) {
                     $numFmtsNode = new SimpleXMLElement($xmlReader->readOuterXml());
diff --git a/src/Spout/Writer/ODS/Internal/Worksheet.php b/src/Spout/Writer/ODS/Internal/Worksheet.php
index 7a0df1a..cec30af 100644
--- a/src/Spout/Writer/ODS/Internal/Worksheet.php
+++ b/src/Spout/Writer/ODS/Internal/Worksheet.php
@@ -47,7 +47,7 @@ class Worksheet implements WorksheetInterface
     {
         $this->externalSheet = $externalSheet;
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $this->stringsEscaper = new \Box\Spout\Common\Escaper\ODS();
+        $this->stringsEscaper = \Box\Spout\Common\Escaper\ODS::getInstance();
         $this->worksheetFilePath = $worksheetFilesFolder . '/sheet' . $externalSheet->getIndex() . '.xml';
 
         $this->stringHelper = new StringHelper();
diff --git a/src/Spout/Writer/XLSX/Helper/FileSystemHelper.php b/src/Spout/Writer/XLSX/Helper/FileSystemHelper.php
index 59df98a..786e62e 100644
--- a/src/Spout/Writer/XLSX/Helper/FileSystemHelper.php
+++ b/src/Spout/Writer/XLSX/Helper/FileSystemHelper.php
@@ -284,7 +284,7 @@ EOD;
 EOD;
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
 
         /** @var Worksheet $worksheet */
         foreach ($worksheets as $worksheet) {
diff --git a/src/Spout/Writer/XLSX/Helper/SharedStringsHelper.php b/src/Spout/Writer/XLSX/Helper/SharedStringsHelper.php
index 9d9639d..292b663 100644
--- a/src/Spout/Writer/XLSX/Helper/SharedStringsHelper.php
+++ b/src/Spout/Writer/XLSX/Helper/SharedStringsHelper.php
@@ -49,7 +49,7 @@ EOD;
         fwrite($this->sharedStringsFilePointer, $header);
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $this->stringsEscaper = new \Box\Spout\Common\Escaper\XLSX();
+        $this->stringsEscaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
     }
 
     /**
diff --git a/src/Spout/Writer/XLSX/Internal/Worksheet.php b/src/Spout/Writer/XLSX/Internal/Worksheet.php
index ab959c6..2439db1 100644
--- a/src/Spout/Writer/XLSX/Internal/Worksheet.php
+++ b/src/Spout/Writer/XLSX/Internal/Worksheet.php
@@ -56,7 +56,7 @@ EOD;
         $this->shouldUseInlineStrings = $shouldUseInlineStrings;
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $this->stringsEscaper = new \Box\Spout\Common\Escaper\XLSX();
+        $this->stringsEscaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
 
         $this->worksheetFilePath = $worksheetFilesFolder . '/' . strtolower($this->externalSheet->getName()) . '.xml';
         $this->startSheet();
diff --git a/tests/Spout/Common/Escaper/XLSXTest.php b/tests/Spout/Common/Escaper/XLSXTest.php
index 7c0b2db..289e2a2 100644
--- a/tests/Spout/Common/Escaper/XLSXTest.php
+++ b/tests/Spout/Common/Escaper/XLSXTest.php
@@ -35,7 +35,7 @@ class XLSXTest extends \PHPUnit_Framework_TestCase
     public function testEscape($stringToEscape, $expectedEscapedString)
     {
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
         $escapedString = $escaper->escape($stringToEscape);
 
         $this->assertEquals($expectedEscapedString, $escapedString, 'Incorrect escaped string');
@@ -67,7 +67,7 @@ class XLSXTest extends \PHPUnit_Framework_TestCase
     public function testUnescape($stringToUnescape, $expectedUnescapedString)
     {
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
         $unescapedString = $escaper->unescape($stringToUnescape);
 
         $this->assertEquals($expectedUnescapedString, $unescapedString, 'Incorrect escaped string');
diff --git a/tests/Spout/Reader/Wrapper/XMLReaderTest.php b/tests/Spout/Reader/Wrapper/XMLReaderTest.php
index a4deacd..b16c648 100644
--- a/tests/Spout/Reader/Wrapper/XMLReaderTest.php
+++ b/tests/Spout/Reader/Wrapper/XMLReaderTest.php
@@ -20,12 +20,11 @@ class XMLReaderTest extends \PHPUnit_Framework_TestCase
     public function testOpenShouldFailIfFileInsideZipDoesNotExist()
     {
         $resourcePath = $this->getResourcePath('one_sheet_with_inline_strings.xlsx');
-        $nonExistingXMLFilePath = 'zip://' . $resourcePath . '#path/to/fake/file.xml';
 
         $xmlReader = new XMLReader();
 
         // using "@" to prevent errors/warning to be displayed
-        $wasOpenSuccessful = @$xmlReader->open($nonExistingXMLFilePath);
+        $wasOpenSuccessful = @$xmlReader->openFileInZip($resourcePath, 'path/to/fake/file.xml');
 
         $this->assertTrue($wasOpenSuccessful === false);
     }
@@ -72,10 +71,9 @@ class XMLReaderTest extends \PHPUnit_Framework_TestCase
     public function testReadShouldThrowExceptionOnError()
     {
         $resourcePath = $this->getResourcePath('one_sheet_with_invalid_xml_characters.xlsx');
-        $sheetDataXMLFilePath = 'zip://' . $resourcePath . '#xl/worksheets/sheet1.xml';
 
         $xmlReader = new XMLReader();
-        if ($xmlReader->open($sheetDataXMLFilePath) === false) {
+        if ($xmlReader->openFileInZip($resourcePath, 'xl/worksheets/sheet1.xml') === false) {
             $this->fail();
         }
 
@@ -95,43 +93,13 @@ class XMLReaderTest extends \PHPUnit_Framework_TestCase
         // The sharedStrings.xml file in "attack_billion_laughs.xlsx" contains
         // a doctype element that causes read errors
         $resourcePath = $this->getResourcePath('attack_billion_laughs.xlsx');
-        $sheetDataXMLFilePath = 'zip://' . $resourcePath . '#xl/sharedStrings.xml';
 
         $xmlReader = new XMLReader();
-        if ($xmlReader->open($sheetDataXMLFilePath) !== false) {
+        if ($xmlReader->openFileInZip($resourcePath, 'xl/sharedStrings.xml') !== false) {
             @$xmlReader->next('sst');
         }
     }
 
-    /**
-     * @return array
-     */
-    public function dataProviderForTestIsZipStream()
-    {
-        return [
-            ['/absolute/path/to/file.xlsx', false],
-            ['relative/path/to/file.xlsx', false],
-            ['php://temp', false],
-            ['zip:///absolute/path/to/file.xlsx', true],
-            ['zip://relative/path/to/file.xlsx', true],
-        ];
-    }
-
-    /**
-     * @dataProvider dataProviderForTestIsZipStream
-     *
-     * @param string $URI
-     * @param bool $expectedResult
-     * @return void
-     */
-    public function testIsZipStream($URI, $expectedResult)
-    {
-        $xmlReader = new XMLReader();
-        $isZipStream = \ReflectionHelper::callMethodOnObject($xmlReader, 'isZipStream', $URI);
-
-        $this->assertEquals($expectedResult, $isZipStream);
-    }
-
     /**
      * @return array
      */
@@ -167,35 +135,70 @@ class XMLReaderTest extends \PHPUnit_Framework_TestCase
     /**
      * @return array
      */
-    public function dataProviderForTestConvertURIToUseRealPath()
+    public function dataProviderForTestGetRealPathURIForFileInZip()
     {
         $tempFolder = realpath(sys_get_temp_dir());
+        $expectedRealPathURI = 'zip://' . $tempFolder . '/test.xlsx#test.xml';
 
         return [
-            ['/../../../' . $tempFolder . '/test.xlsx', $tempFolder . '/test.xlsx'],
-            [$tempFolder . '/test.xlsx', $tempFolder . '/test.xlsx'],
-            ['zip://' . $tempFolder . '/test.xlsx#test.xml', 'zip://' . $tempFolder . '/test.xlsx#test.xml'],
-            ['zip:///../../../' . $tempFolder . '/test.xlsx#test.xml', 'zip://' . $tempFolder . '/test.xlsx#test.xml'],
+            [$tempFolder, "$tempFolder/test.xlsx", 'test.xml', $expectedRealPathURI],
+            [$tempFolder, "/../../../$tempFolder/test.xlsx", 'test.xml', $expectedRealPathURI],
         ];
     }
 
     /**
-     * @dataProvider dataProviderForTestConvertURIToUseRealPath
+     * @dataProvider dataProviderForTestGetRealPathURIForFileInZip
      *
-     * @param string $URI
-     * @param string $expectedConvertedURI
+     * @param string $tempFolder
+     * @param string $zipFilePath
+     * @param string $fileInsideZipPath
+     * @param string $expectedRealPathURI
      * @return void
      */
-    public function testConvertURIToUseRealPath($URI, $expectedConvertedURI)
+    public function testGetRealPathURIForFileInZip($tempFolder, $zipFilePath, $fileInsideZipPath, $expectedRealPathURI)
     {
-        $tempFolder = sys_get_temp_dir();
         touch($tempFolder . '/test.xlsx');
 
         $xmlReader = new XMLReader();
-        $convertedURI = \ReflectionHelper::callMethodOnObject($xmlReader, 'convertURIToUseRealPath', $URI);
+        $realPathURI = \ReflectionHelper::callMethodOnObject($xmlReader, 'getRealPathURIForFileInZip', $zipFilePath, $fileInsideZipPath);
 
-        $this->assertEquals($expectedConvertedURI, $convertedURI);
+        $this->assertEquals($expectedRealPathURI, $realPathURI);
 
         unlink($tempFolder . '/test.xlsx');
     }
+
+    /**
+     * @return array
+     */
+    public function dataProviderForTestIsPositionedOnStartingAndEndingNode()
+    {
+        return [
+            ['<test></test>'], // not prefixed
+            ['<x:test xmlns:x="foo"></x:test>'], // prefixed
+        ];
+    }
+
+    /**
+     * @dataProvider dataProviderForTestIsPositionedOnStartingAndEndingNode
+     *
+     * @param string $testXML
+     * @return void
+     */
+    public function testIsPositionedOnStartingAndEndingNode($testXML)
+    {
+        $xmlReader = new XMLReader();
+        $xmlReader->XML($testXML);
+
+        // the first read moves the pointer to "<test>"
+        $xmlReader->read();
+        $this->assertTrue($xmlReader->isPositionedOnStartingNode('test'));
+        $this->assertFalse($xmlReader->isPositionedOnEndingNode('test'));
+
+        // the seconds read moves the pointer to "</test>"
+        $xmlReader->read();
+        $this->assertFalse($xmlReader->isPositionedOnStartingNode('test'));
+        $this->assertTrue($xmlReader->isPositionedOnEndingNode('test'));
+
+        $xmlReader->close();
+    }
 }
diff --git a/tests/Spout/Reader/XLSX/Helper/CellValueFormatterTest.php b/tests/Spout/Reader/XLSX/Helper/CellValueFormatterTest.php
index 92831ab..96c71a9 100644
--- a/tests/Spout/Reader/XLSX/Helper/CellValueFormatterTest.php
+++ b/tests/Spout/Reader/XLSX/Helper/CellValueFormatterTest.php
@@ -87,6 +87,10 @@ class CellValueFormatterTest extends \PHPUnit_Framework_TestCase
      */
     public function dataProviderForTestFormatNumericCellValueWithNumbers()
     {
+        // Some test values exceed PHP_INT_MAX on 32-bit PHP. They are
+        // therefore converted to as doubles automatically by PHP.
+        $expectedBigNumberType = (PHP_INT_SIZE < 8 ? 'double' : 'integer');
+
         return [
             [42, 42, 'integer'],
             [42.5, 42.5, 'double'],
@@ -94,8 +98,8 @@ class CellValueFormatterTest extends \PHPUnit_Framework_TestCase
             [-42.5, -42.5, 'double'],
             ['42', 42, 'integer'],
             ['42.5', 42.5, 'double'],
-            [865640023012945, 865640023012945, 'integer'],
-            ['865640023012945', 865640023012945, 'integer'],
+            [865640023012945, 865640023012945, $expectedBigNumberType],
+            ['865640023012945', 865640023012945, $expectedBigNumberType],
             [865640023012945.5, 865640023012945.5, 'double'],
             ['865640023012945.5', 865640023012945.5, 'double'],
             [PHP_INT_MAX, PHP_INT_MAX, 'integer'],
diff --git a/tests/Spout/Reader/XLSX/ReaderTest.php b/tests/Spout/Reader/XLSX/ReaderTest.php
index 8620ed5..2703799 100644
--- a/tests/Spout/Reader/XLSX/ReaderTest.php
+++ b/tests/Spout/Reader/XLSX/ReaderTest.php
@@ -95,6 +95,23 @@ class ReaderTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals($expectedRows, $allRows);
     }
 
+    /**
+     * @return void
+     */
+    public function testReadShouldSupportPrefixedXMLFiles()
+    {
+        // The XML files of this spreadsheet are prefixed.
+        // For instance, they use "<x:sheet>" instead of "<sheet>", etc.
+        $allRows = $this->getAllRowsForFile('sheet_with_prefixed_xml_files.xlsx');
+
+        $expectedRows = [
+            ['s1 - A1', 's1 - B1', 's1 - C1'],
+            ['s1 - A2', 's1 - B2', 's1 - C2'],
+            ['s1 - A3', 's1 - B3', 's1 - C3'],
+        ];
+        $this->assertEquals($expectedRows, $allRows);
+    }
+
     /**
      * @return void
      */
diff --git a/tests/Spout/Writer/ODS/WriterTest.php b/tests/Spout/Writer/ODS/WriterTest.php
index 4c67e4e..43383e4 100644
--- a/tests/Spout/Writer/ODS/WriterTest.php
+++ b/tests/Spout/Writer/ODS/WriterTest.php
@@ -538,10 +538,9 @@ class WriterTest extends \PHPUnit_Framework_TestCase
     private function moveReaderToCorrectTableNode($fileName, $sheetIndex)
     {
         $resourcePath = $this->getGeneratedResourcePath($fileName);
-        $pathToSheetFile = $resourcePath . '#content.xml';
 
         $xmlReader = new XMLReader();
-        $xmlReader->open('zip://' . $pathToSheetFile);
+        $xmlReader->openFileInZip($resourcePath, 'content.xml');
         $xmlReader->readUntilNodeFound('table:table');
 
         for ($i = 1; $i < $sheetIndex; $i++) {
diff --git a/tests/Spout/Writer/ODS/WriterWithStyleTest.php b/tests/Spout/Writer/ODS/WriterWithStyleTest.php
index cc3fc50..9888bfc 100644
--- a/tests/Spout/Writer/ODS/WriterWithStyleTest.php
+++ b/tests/Spout/Writer/ODS/WriterWithStyleTest.php
@@ -296,17 +296,18 @@ class WriterWithStyleTest extends \PHPUnit_Framework_TestCase
         $cellElements = [];
 
         $resourcePath = $this->getGeneratedResourcePath($fileName);
-        $pathToStylesXmlFile = $resourcePath . '#content.xml';
 
-        $xmlReader = new \XMLReader();
-        $xmlReader->open('zip://' . $pathToStylesXmlFile);
+        $xmlReader = new XMLReader();
+        $xmlReader->openFileInZip($resourcePath, 'content.xml');
 
         while ($xmlReader->read()) {
-            if ($xmlReader->nodeType === \XMLReader::ELEMENT && $xmlReader->name === 'table:table-cell' && $xmlReader->getAttribute('office:value-type') !== null) {
+            if ($xmlReader->isPositionedOnStartingNode('table:table-cell') && $xmlReader->getAttribute('office:value-type') !== null) {
                 $cellElements[] = $xmlReader->expand();
             }
         }
 
+        $xmlReader->close();
+        
         return $cellElements;
     }
 
@@ -319,17 +320,18 @@ class WriterWithStyleTest extends \PHPUnit_Framework_TestCase
         $cellStyleElements = [];
 
         $resourcePath = $this->getGeneratedResourcePath($fileName);
-        $pathToStylesXmlFile = $resourcePath . '#content.xml';
 
-        $xmlReader = new \XMLReader();
-        $xmlReader->open('zip://' . $pathToStylesXmlFile);
+        $xmlReader = new XMLReader();
+        $xmlReader->openFileInZip($resourcePath, 'content.xml');
 
         while ($xmlReader->read()) {
-            if ($xmlReader->nodeType === \XMLReader::ELEMENT && $xmlReader->name === 'style:style' && $xmlReader->getAttribute('style:family') === 'table-cell') {
+            if ($xmlReader->isPositionedOnStartingNode('style:style') && $xmlReader->getAttribute('style:family') === 'table-cell') {
                 $cellStyleElements[] = $xmlReader->expand();
             }
         }
 
+        $xmlReader->close();
+        
         return $cellStyleElements;
     }
 
@@ -341,10 +343,9 @@ class WriterWithStyleTest extends \PHPUnit_Framework_TestCase
     private function getXmlSectionFromStylesXmlFile($fileName, $section)
     {
         $resourcePath = $this->getGeneratedResourcePath($fileName);
-        $pathToStylesXmlFile = $resourcePath . '#styles.xml';
 
         $xmlReader = new XMLReader();
-        $xmlReader->open('zip://' . $pathToStylesXmlFile);
+        $xmlReader->openFileInZip($resourcePath, 'styles.xml');
         $xmlReader->readUntilNodeFound($section);
 
         return $xmlReader->expand();
diff --git a/tests/Spout/Writer/XLSX/WriterWithStyleTest.php b/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
index 9a531b9..d43b566 100644
--- a/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
+++ b/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
@@ -293,13 +293,16 @@ class WriterWithStyleTest extends \PHPUnit_Framework_TestCase
     private function getXmlSectionFromStylesXmlFile($fileName, $section)
     {
         $resourcePath = $this->getGeneratedResourcePath($fileName);
-        $pathToStylesXmlFile = $resourcePath . '#xl/styles.xml';
 
         $xmlReader = new XMLReader();
-        $xmlReader->open('zip://' . $pathToStylesXmlFile);
+        $xmlReader->openFileInZip($resourcePath, 'xl/styles.xml');
         $xmlReader->readUntilNodeFound($section);
 
-        return $xmlReader->expand();
+        $xmlSection = $xmlReader->expand();
+
+        $xmlReader->close();
+
+        return $xmlSection;
     }
 
     /**
@@ -311,17 +314,18 @@ class WriterWithStyleTest extends \PHPUnit_Framework_TestCase
         $cellElements = [];
 
         $resourcePath = $this->getGeneratedResourcePath($fileName);
-        $pathToStylesXmlFile = $resourcePath . '#xl/worksheets/sheet1.xml';
 
-        $xmlReader = new \XMLReader();
-        $xmlReader->open('zip://' . $pathToStylesXmlFile);
+        $xmlReader = new XMLReader();
+        $xmlReader->openFileInZip($resourcePath, 'xl/worksheets/sheet1.xml');
 
         while ($xmlReader->read()) {
-            if ($xmlReader->nodeType === \XMLReader::ELEMENT && $xmlReader->name === 'c') {
+            if ($xmlReader->isPositionedOnStartingNode('c')) {
                 $cellElements[] = $xmlReader->expand();
             }
         }
 
+        $xmlReader->close();
+
         return $cellElements;
     }
 
diff --git a/tests/resources/xlsx/sheet_with_prefixed_xml_files.xlsx b/tests/resources/xlsx/sheet_with_prefixed_xml_files.xlsx
new file mode 100644
index 0000000..d8bbc39
Binary files /dev/null and b/tests/resources/xlsx/sheet_with_prefixed_xml_files.xlsx differ