diff --git a/src/PhpSpreadsheet/Cell/Cell.php b/src/PhpSpreadsheet/Cell/Cell.php
index ae075003..ac14573f 100644
--- a/src/PhpSpreadsheet/Cell/Cell.php
+++ b/src/PhpSpreadsheet/Cell/Cell.php
@@ -6,7 +6,8 @@ use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
 use PhpOffice\PhpSpreadsheet\Collection\Cells;
 use PhpOffice\PhpSpreadsheet\Exception;
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
-use PhpOffice\PhpSpreadsheet\Style;
+use PhpOffice\PhpSpreadsheet\Style\NumberFormat;
+use PhpOffice\PhpSpreadsheet\Style\Style;
 use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
 
 class Cell
@@ -167,7 +168,7 @@ class Cell
      */
     public function getFormattedValue()
     {
-        return (string) Style\NumberFormat::toFormattedString(
+        return (string) NumberFormat::toFormattedString(
             $this->getCalculatedValue(),
             $this->getStyle()
                 ->getNumberFormat()->getFormatCode()
diff --git a/src/PhpSpreadsheet/Worksheet/Worksheet.php b/src/PhpSpreadsheet/Worksheet/Worksheet.php
index d74de3e1..10a49c30 100644
--- a/src/PhpSpreadsheet/Worksheet/Worksheet.php
+++ b/src/PhpSpreadsheet/Worksheet/Worksheet.php
@@ -1343,7 +1343,7 @@ class Worksheet implements IComparable
      * Get row dimension at a specific row.
      *
      * @param int $pRow Numeric index of the row
-     * @param mixed $create
+     * @param bool $create
      *
      * @return RowDimension
      */
@@ -1369,7 +1369,7 @@ class Worksheet implements IComparable
      * Get column dimension at a specific column.
      *
      * @param string $pColumn String index of the column eg: 'A'
-     * @param mixed $create
+     * @param bool $create
      *
      * @return ColumnDimension
      */
@@ -1910,7 +1910,7 @@ class Worksheet implements IComparable
     /**
      * Set AutoFilter.
      *
-     * @param string|Worksheet\AutoFilter $pValue
+     * @param AutoFilter|string $pValue
      *            A simple string containing a Cell range like 'A1:E10' is permitted for backward compatibility
      *
      * @throws Exception
@@ -1919,7 +1919,6 @@ class Worksheet implements IComparable
      */
     public function setAutoFilter($pValue)
     {
-        $pValue = strtoupper($pValue);
         if (is_string($pValue)) {
             $this->autoFilter->setRange($pValue);
         } elseif (is_object($pValue) && ($pValue instanceof AutoFilter)) {
diff --git a/src/PhpSpreadsheet/Writer/Html.php b/src/PhpSpreadsheet/Writer/Html.php
index 44527bd1..33533f2c 100644
--- a/src/PhpSpreadsheet/Writer/Html.php
+++ b/src/PhpSpreadsheet/Writer/Html.php
@@ -1164,7 +1164,7 @@ class Html extends BaseWriter implements IWriter
      * @param Worksheet $pSheet \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet
      * @param array $pValues Array containing cells in a row
      * @param int $pRow Row number (0-based)
-     * @param mixed $cellType eg: 'td'
+     * @param string $cellType eg: 'td'
      *
      * @throws WriterException
      *
diff --git a/src/PhpSpreadsheet/Writer/Ods/MetaInf.php b/src/PhpSpreadsheet/Writer/Ods/MetaInf.php
index 7336b4ea..1ec9d1eb 100644
--- a/src/PhpSpreadsheet/Writer/Ods/MetaInf.php
+++ b/src/PhpSpreadsheet/Writer/Ods/MetaInf.php
@@ -3,7 +3,6 @@
 namespace PhpOffice\PhpSpreadsheet\Writer\Ods;
 
 use PhpOffice\PhpSpreadsheet\Shared\XMLWriter;
-use PhpOffice\PhpSpreadsheet\Spreadsheet;
 
 class MetaInf extends WriterPart
 {
diff --git a/src/PhpSpreadsheet/Writer/Xls/Workbook.php b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
index fa901981..d8cc0464 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Workbook.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
@@ -224,8 +224,8 @@ class Workbook extends BIFFwriter
      *
      * @param Style
      * @param bool Is it a style XF?
-     * @param mixed $style
-     * @param mixed $isStyleXf
+     * @param Style $style
+     * @param bool $isStyleXf
      *
      * @return int Index to XF record
      */
@@ -683,7 +683,7 @@ class Workbook extends BIFFwriter
      *
      * @param string $name The name in UTF-8
      * @param string $formulaData The binary formula data
-     * @param string $sheetIndex 1-based sheet index the defined name applies to. 0 = global
+     * @param int $sheetIndex 1-based sheet index the defined name applies to. 0 = global
      * @param bool $isBuiltIn Built-in name?
      *
      * @return string Complete binary record data
diff --git a/src/PhpSpreadsheet/Writer/Xls/Worksheet.php b/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
index 6e9d8fdf..47b0ff93 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
@@ -176,7 +176,7 @@ class Worksheet extends BIFFwriter
     /**
      * Sheet object.
      *
-     * @var Worksheet
+     * @var \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet
      */
     public $phpSheet;
 
@@ -214,16 +214,15 @@ class Worksheet extends BIFFwriter
     /**
      * Constructor.
      *
-     * @param int &$str_total Total number of strings
-     * @param int &$str_unique Total number of unique strings
+     * @param int $str_total Total number of strings
+     * @param int $str_unique Total number of unique strings
      * @param array &$str_table String Table
      * @param array &$colors Colour Table
-     * @param mixed $parser The formula parser created for the Workbook
+     * @param Parser $parser The formula parser created for the Workbook
      * @param bool $preCalculateFormulas Flag indicating whether formulas should be calculated or just written
-     * @param string $phpSheet The worksheet to write
-     * @param Worksheet $phpSheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $phpSheet The worksheet to write
      */
-    public function __construct(&$str_total, &$str_unique, &$str_table, &$colors, $parser, $preCalculateFormulas, $phpSheet)
+    public function __construct(&$str_total, &$str_unique, &$str_table, &$colors, Parser $parser, $preCalculateFormulas, \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $phpSheet)
     {
         // It needs to call its parent's constructor explicitly
         parent::__construct();
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
index 1d8e0bd8..f250cdda 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
@@ -204,7 +204,7 @@ class Chart extends WriterPart
      * Write Chart Plot Area.
      *
      * @param XMLWriter $objWriter XML Writer
-     * @param Worksheet $pSheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pSheet
      * @param PlotArea $plotArea
      * @param Title $xAxisLabel
      * @param Title $yAxisLabel
@@ -394,11 +394,11 @@ class Chart extends WriterPart
      * @param string $id1
      * @param string $id2
      * @param bool $isMultiLevelSeries
-     * @param mixed $yAxis
+     * @param Axis $yAxis
      *
      * @throws WriterException
      */
-    private function writeCategoryAxis($objWriter, $xAxisLabel, $id1, $id2, $isMultiLevelSeries, $yAxis)
+    private function writeCategoryAxis($objWriter, $xAxisLabel, $id1, $id2, $isMultiLevelSeries, Axis $yAxis)
     {
         $objWriter->startElement('c:catAx');
 
@@ -515,13 +515,13 @@ class Chart extends WriterPart
      * @param string $id1
      * @param string $id2
      * @param bool $isMultiLevelSeries
-     * @param mixed $xAxis
-     * @param mixed $majorGridlines
-     * @param mixed $minorGridlines
+     * @param Axis $xAxis
+     * @param GridLines $majorGridlines
+     * @param GridLines $minorGridlines
      *
      * @throws WriterException
      */
-    private function writeValueAxis($objWriter, $yAxisLabel, $groupType, $id1, $id2, $isMultiLevelSeries, $xAxis, $majorGridlines, $minorGridlines)
+    private function writeValueAxis($objWriter, $yAxisLabel, $groupType, $id1, $id2, $isMultiLevelSeries, Axis $xAxis, GridLines $majorGridlines, GridLines $minorGridlines)
     {
         $objWriter->startElement('c:valAx');
 
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Comments.php b/src/PhpSpreadsheet/Writer/Xlsx/Comments.php
index bb24c884..f1f0400f 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Comments.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Comments.php
@@ -11,7 +11,7 @@ class Comments extends WriterPart
     /**
      * Write comments to XML format.
      *
-     * @param Worksheet $pWorksheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet
      *
      * @throws \PhpOffice\PhpSpreadsheet\Writer\Exception
      *
@@ -94,7 +94,7 @@ class Comments extends WriterPart
     /**
      * Write VML comments to XML format.
      *
-     * @param Worksheet $pWorksheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet
      *
      * @throws \PhpOffice\PhpSpreadsheet\Writer\Exception
      *
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php b/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php
index 3bf30588..b710e132 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php
@@ -14,7 +14,7 @@ class Drawing extends WriterPart
     /**
      * Write drawings to XML format.
      *
-     * @param Worksheet $pWorksheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet
      * @param bool $includeCharts Flag indicating if we should include drawing details for charts
      *
      * @throws WriterException
@@ -271,7 +271,7 @@ class Drawing extends WriterPart
     /**
      * Write VML header/footer images to XML format.
      *
-     * @param Worksheet $pWorksheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet
      *
      * @throws WriterException
      *
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Rels.php b/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
index 0d1610a1..e5d2aa53 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
@@ -168,7 +168,7 @@ class Rels extends WriterPart
      *     rId1                 - Drawings
      *  rId_hyperlink_x     - Hyperlinks
      *
-     * @param Worksheet $pWorksheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet
      * @param int $pWorksheetId
      * @param bool $includeCharts Flag indicating if we should write charts
      *
@@ -263,7 +263,7 @@ class Rels extends WriterPart
     /**
      * Write drawing relationships to XML format.
      *
-     * @param Worksheet $pWorksheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet
      * @param int &$chartRef Chart ID
      * @param bool $includeCharts Flag indicating if we should write charts
      *
@@ -330,7 +330,7 @@ class Rels extends WriterPart
     /**
      * Write header/footer drawing relationships to XML format.
      *
-     * @param Worksheet $pWorksheet
+     * @param \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $pWorksheet
      *
      * @throws WriterException
      *
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
index 12668079..3a2ceabe 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
@@ -31,96 +31,92 @@ class Worksheet extends WriterPart
      *
      * @return string XML Output
      */
-    public function writeWorksheet($pSheet = null, $pStringTable = null, $includeCharts = false)
+    public function writeWorksheet(PhpspreadsheetWorksheet $pSheet, $pStringTable = null, $includeCharts = false)
     {
-        if ($pSheet !== null) {
-            // Create XML writer
-            $objWriter = null;
-            if ($this->getParentWriter()->getUseDiskCaching()) {
-                $objWriter = new XMLWriter(XMLWriter::STORAGE_DISK, $this->getParentWriter()->getDiskCachingDirectory());
-            } else {
-                $objWriter = new XMLWriter(XMLWriter::STORAGE_MEMORY);
-            }
-
-            // XML header
-            $objWriter->startDocument('1.0', 'UTF-8', 'yes');
-
-            // Worksheet
-            $objWriter->startElement('worksheet');
-            $objWriter->writeAttribute('xml:space', 'preserve');
-            $objWriter->writeAttribute('xmlns', 'http://schemas.openxmlformats.org/spreadsheetml/2006/main');
-            $objWriter->writeAttribute('xmlns:r', 'http://schemas.openxmlformats.org/officeDocument/2006/relationships');
-
-            // sheetPr
-            $this->writeSheetPr($objWriter, $pSheet);
-
-            // Dimension
-            $this->writeDimension($objWriter, $pSheet);
-
-            // sheetViews
-            $this->writeSheetViews($objWriter, $pSheet);
-
-            // sheetFormatPr
-            $this->writeSheetFormatPr($objWriter, $pSheet);
-
-            // cols
-            $this->writeCols($objWriter, $pSheet);
-
-            // sheetData
-            $this->writeSheetData($objWriter, $pSheet, $pStringTable);
-
-            // sheetProtection
-            $this->writeSheetProtection($objWriter, $pSheet);
-
-            // protectedRanges
-            $this->writeProtectedRanges($objWriter, $pSheet);
-
-            // autoFilter
-            $this->writeAutoFilter($objWriter, $pSheet);
-
-            // mergeCells
-            $this->writeMergeCells($objWriter, $pSheet);
-
-            // conditionalFormatting
-            $this->writeConditionalFormatting($objWriter, $pSheet);
-
-            // dataValidations
-            $this->writeDataValidations($objWriter, $pSheet);
-
-            // hyperlinks
-            $this->writeHyperlinks($objWriter, $pSheet);
-
-            // Print options
-            $this->writePrintOptions($objWriter, $pSheet);
-
-            // Page margins
-            $this->writePageMargins($objWriter, $pSheet);
-
-            // Page setup
-            $this->writePageSetup($objWriter, $pSheet);
-
-            // Header / footer
-            $this->writeHeaderFooter($objWriter, $pSheet);
-
-            // Breaks
-            $this->writeBreaks($objWriter, $pSheet);
-
-            // Drawings and/or Charts
-            $this->writeDrawings($objWriter, $pSheet, $includeCharts);
-
-            // LegacyDrawing
-            $this->writeLegacyDrawing($objWriter, $pSheet);
-
-            // LegacyDrawingHF
-            $this->writeLegacyDrawingHF($objWriter, $pSheet);
-
-            $objWriter->endElement();
-
-            // Return
-            return $objWriter->getData();
+        // Create XML writer
+        $objWriter = null;
+        if ($this->getParentWriter()->getUseDiskCaching()) {
+            $objWriter = new XMLWriter(XMLWriter::STORAGE_DISK, $this->getParentWriter()->getDiskCachingDirectory());
+        } else {
+            $objWriter = new XMLWriter(XMLWriter::STORAGE_MEMORY);
         }
 
-        throw new WriterException('Invalid \\PhpOffice\\PhpSpreadsheet\\Worksheet\\Worksheet object passed.');
+        // XML header
+        $objWriter->startDocument('1.0', 'UTF-8', 'yes');
+
+        // Worksheet
+        $objWriter->startElement('worksheet');
+        $objWriter->writeAttribute('xml:space', 'preserve');
+        $objWriter->writeAttribute('xmlns', 'http://schemas.openxmlformats.org/spreadsheetml/2006/main');
+        $objWriter->writeAttribute('xmlns:r', 'http://schemas.openxmlformats.org/officeDocument/2006/relationships');
+
+        // sheetPr
+        $this->writeSheetPr($objWriter, $pSheet);
+
+        // Dimension
+        $this->writeDimension($objWriter, $pSheet);
+
+        // sheetViews
+        $this->writeSheetViews($objWriter, $pSheet);
+
+        // sheetFormatPr
+        $this->writeSheetFormatPr($objWriter, $pSheet);
+
+        // cols
+        $this->writeCols($objWriter, $pSheet);
+
+        // sheetData
+        $this->writeSheetData($objWriter, $pSheet, $pStringTable);
+
+        // sheetProtection
+        $this->writeSheetProtection($objWriter, $pSheet);
+
+        // protectedRanges
+        $this->writeProtectedRanges($objWriter, $pSheet);
+
+        // autoFilter
+        $this->writeAutoFilter($objWriter, $pSheet);
+
+        // mergeCells
+        $this->writeMergeCells($objWriter, $pSheet);
+
+        // conditionalFormatting
+        $this->writeConditionalFormatting($objWriter, $pSheet);
+
+        // dataValidations
+        $this->writeDataValidations($objWriter, $pSheet);
+
+        // hyperlinks
+        $this->writeHyperlinks($objWriter, $pSheet);
+
+        // Print options
+        $this->writePrintOptions($objWriter, $pSheet);
+
+        // Page margins
+        $this->writePageMargins($objWriter, $pSheet);
+
+        // Page setup
+        $this->writePageSetup($objWriter, $pSheet);
+
+        // Header / footer
+        $this->writeHeaderFooter($objWriter, $pSheet);
+
+        // Breaks
+        $this->writeBreaks($objWriter, $pSheet);
+
+        // Drawings and/or Charts
+        $this->writeDrawings($objWriter, $pSheet, $includeCharts);
+
+        // LegacyDrawing
+        $this->writeLegacyDrawing($objWriter, $pSheet);
+
+        // LegacyDrawingHF
+        $this->writeLegacyDrawingHF($objWriter, $pSheet);
+
+        $objWriter->endElement();
+
+        // Return
+        return $objWriter->getData();
     }
 
     /**
@@ -531,7 +527,7 @@ class Worksheet extends WriterPart
      * Write DataValidations.
      *
      * @param XMLWriter $objWriter XML Writer
-     * @param \PhpOffice\PhpSpreadsheet\Worksheet\PhpspreadsheetWorksheet $pSheet Worksheet
+     * @param PhpspreadsheetWorksheet $pSheet Worksheet
      *
      * @throws WriterException
      */
@@ -697,7 +693,7 @@ class Worksheet extends WriterPart
      * Write PrintOptions.
      *
      * @param XMLWriter $objWriter XML Writer
-     * @param \PhpOffice\PhpSpreadsheet\Worksheet\PhpspreadsheetWorksheet $pSheet Worksheet
+     * @param PhpspreadsheetWorksheet $pSheet Worksheet
      *
      * @throws WriterException
      */
@@ -724,7 +720,7 @@ class Worksheet extends WriterPart
      * Write PageMargins.
      *
      * @param XMLWriter $objWriter XML Writer
-     * @param \PhpOffice\PhpSpreadsheet\Worksheet\PhpspreadsheetWorksheet $pSheet Worksheet
+     * @param PhpspreadsheetWorksheet $pSheet Worksheet
      *
      * @throws WriterException
      */
@@ -901,7 +897,7 @@ class Worksheet extends WriterPart
      * Write Breaks.
      *
      * @param XMLWriter $objWriter XML Writer
-     * @param \PhpOffice\PhpSpreadsheet\Worksheet\PhpspreadsheetWorksheet $pSheet Worksheet
+     * @param PhpspreadsheetWorksheet $pSheet Worksheet
      *
      * @throws WriterException
      */
@@ -1048,7 +1044,6 @@ class Worksheet extends WriterPart
      * @param XMLWriter $objWriter XML Writer
      * @param PhpspreadsheetWorksheet $pSheet Worksheet
      * @param Cell $pCellAddress Cell Address
-     * @param string[] $pStringTable String table
      * @param string[] $pFlippedStringTable String table (flipped), for faster index searching
      *
      * @throws WriterException
@@ -1167,7 +1162,7 @@ class Worksheet extends WriterPart
      * Write Drawings.
      *
      * @param XMLWriter $objWriter XML Writer
-     * @param \PhpOffice\PhpSpreadsheet\Worksheet\PhpspreadsheetWorksheet $pSheet Worksheet
+     * @param PhpspreadsheetWorksheet $pSheet Worksheet
      * @param bool $includeCharts Flag indicating if we should include drawing details for charts
      *
      * @throws WriterException