diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs
index 13a6420..0eb27b1 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs
@@ -43,7 +43,9 @@
         }
         public T GetValue<T>() 
         {
-            if (Value is TimeSpan)
+            if (!StringExtensions.IsNullOrWhiteSpace(FormulaA1))
+                return (T)Convert.ChangeType(String.Empty, typeof(T));
+            else if (Value is TimeSpan)
                 if (typeof(T) == typeof(String))
                     return (T)Convert.ChangeType(Value.ToString(), typeof(T));
                 else
@@ -73,43 +75,49 @@
         }
         public String GetFormattedString()
         {
+            String cValue;
+            if (StringExtensions.IsNullOrWhiteSpace(FormulaA1))
+                cValue = cellValue;
+            else
+                cValue = GetString();
+
             if (dataType == XLCellValues.Boolean)
             {
-                return (cellValue != "0").ToString();
+                return (cValue != "0").ToString();
             }
             else if (dataType == XLCellValues.TimeSpan)
             {
-                return cellValue;
+                return cValue;
             }
             else if (dataType == XLCellValues.DateTime || IsDateFormat())
             {
                 Double dTest;
-                if (Double.TryParse(cellValue, out dTest))
+                if (Double.TryParse(cValue, out dTest))
                 {
                     String format = GetFormat();
                     return DateTime.FromOADate(dTest).ToString(format);
                 }
                 else
                 {
-                    return cellValue;
+                    return cValue;
                 }
             }
             else if (dataType == XLCellValues.Number)
             {
                 Double dTest;
-                if (Double.TryParse(cellValue, out dTest))
+                if (Double.TryParse(cValue, out dTest))
                 {
                     String format = GetFormat();
                     return dTest.ToString(format);
                 }
                 else
                 {
-                    return cellValue;
+                    return cValue;
                 }
             }
             else
             {
-                return cellValue;
+                return cValue;
             }
         }
 
@@ -145,28 +153,57 @@
             {
                 var fA1 = FormulaA1;
                 if (!StringExtensions.IsNullOrWhiteSpace(fA1))
-                    return fA1;
+                {
+                    String sName;
+                    String cAddress;
+                    if (fA1.Contains('!'))
+                    {
+                        sName = fA1.Substring(0, fA1.IndexOf('!'));
+                        cAddress = fA1.Substring(fA1.IndexOf('!') + 1);
+                    }
+                    else
+                    {
+                        sName = Worksheet.Name;
+                        cAddress = fA1;
+                    }
 
-                if (dataType == XLCellValues.Boolean)
-                {
-                    return cellValue != "0";
-                }
-                else if (dataType == XLCellValues.DateTime)
-                {
-                    return DateTime.FromOADate(Double.Parse(cellValue));
-                }
-                else if (dataType == XLCellValues.Number)
-                {
-                    return Double.Parse(cellValue);
-                }
-                else if (dataType == XLCellValues.TimeSpan)
-                {
-                    //return (DateTime.FromOADate(Double.Parse(cellValue)) - baseDate);
-                    return TimeSpan.Parse(cellValue);
+                    
+                    if (worksheet.Internals.Workbook.Worksheets.Where(w => w.Name == sName).Any()
+                        && XLAddress.IsValidA1Address(cAddress)
+                        )
+                    {
+                        return worksheet.Internals.Workbook.Worksheet(sName).Cell(cAddress).Value;
+                    }
+                    else
+                    {
+                        return fA1;
+                    }
+
+                    
                 }
                 else
                 {
-                    return cellValue;
+                    if (dataType == XLCellValues.Boolean)
+                    {
+                        return cellValue != "0";
+                    }
+                    else if (dataType == XLCellValues.DateTime)
+                    {
+                        return DateTime.FromOADate(Double.Parse(cellValue));
+                    }
+                    else if (dataType == XLCellValues.Number)
+                    {
+                        return Double.Parse(cellValue);
+                    }
+                    else if (dataType == XLCellValues.TimeSpan)
+                    {
+                        //return (DateTime.FromOADate(Double.Parse(cellValue)) - baseDate);
+                        return TimeSpan.Parse(cellValue);
+                    }
+                    else
+                    {
+                        return cellValue;
+                    }
                 }
             }
             set
@@ -289,7 +326,8 @@
                         {
                             foreach (DataColumn column in (m as DataRow).Table.Columns)
                             {
-                                SetValue(column.ColumnName, fRo, co);
+                                var fieldName = StringExtensions.IsNullOrWhiteSpace(column.Caption) ? column.ColumnName : column.Caption;
+                                SetValue(fieldName, fRo, co);
                                 co++;
                             }
                             co = Address.ColumnNumber;
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCells.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCells.cs
index 92dd533..6e21c2f 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCells.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCells.cs
@@ -35,12 +35,12 @@
                 var cells = from c in worksheet.Internals.CellsCollection
                             where (   !StringExtensions.IsNullOrWhiteSpace(c.Value.InnerText)
                                   || (includeStyles && !c.Value.Style.Equals(worksheet.Style)))
-                                  && rangeAddresses.Where(r=>
+                                  && rangeAddresses.FirstOrDefault(r=>
                                       r.FirstAddress.RowNumber <= c.Key.RowNumber
                                       && r.FirstAddress.ColumnNumber <= c.Key.ColumnNumber
                                       && r.LastAddress.RowNumber >= c.Key.RowNumber
                                       && r.LastAddress.ColumnNumber >= c.Key.ColumnNumber
-                                      ).Any()
+                                      ) != null
                             select (IXLCell)c.Value;
                 foreach (var cell in cells)
                 {
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidation.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidation.cs
index cb7e199..80ef4b1 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidation.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidation.cs
@@ -10,7 +10,7 @@
     public enum XLOperator { EqualTo, NotEqualTo, GreaterThan, LessThan, EqualOrGreaterThan, EqualOrLessThan, Between, NotBetween }
     public interface IXLDataValidation
     {
-        IXLRange Range { get; set; }
+        IXLRanges Ranges { get; set; }
         void Delete();
         void CopyFrom(IXLDataValidation dataValidation);
         Boolean ShowInputMessage { get; set; }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
index 661984c..a5bc443 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
@@ -8,6 +8,5 @@
     public interface IXLDataValidations: IEnumerable<IXLDataValidation>
     {
         void Add(IXLDataValidation dataValidation);
-        void Delete(IXLDataValidation dataValidation);
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidation.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidation.cs
index 84d72e8..15b4865 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidation.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidation.cs
@@ -7,19 +7,25 @@
 {
     internal class XLDataValidation: IXLDataValidation
     {
-        public XLDataValidation(IXLRange range)
+        private XLWorksheet worksheet;
+        public XLDataValidation(IXLRanges ranges, XLWorksheet worksheet)
         {
-            this.Range = range;
+            this.Ranges = ranges;
             this.AllowedValues = XLAllowedValues.AnyValue;
             this.IgnoreBlanks = true;
             ShowErrorMessage = true;
             ShowInputMessage = true;
             InCellDropdown = true;
+            this.worksheet = worksheet;
         }
-        public IXLRange Range { get; set; }
+        public IXLRanges Ranges { get; set; }
+        
         public void Delete()
         {
-            ((XLRange)Range).Worksheet.DataValidations.Delete(this);
+            foreach (var dv in worksheet.DataValidations)
+            { 
+
+            }
         }
         public void CopyFrom(IXLDataValidation dataValidation)
         {
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs
index 3753945..05aba35 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/DataValidation/XLDataValidations.cs
@@ -7,20 +7,20 @@
 {
     internal class XLDataValidations: IXLDataValidations
     {
-        private Dictionary<String, IXLDataValidation> dataValidations = new Dictionary<String, IXLDataValidation>();
+        private List<IXLDataValidation> dataValidations = new List<IXLDataValidation>();
         public void Add(IXLDataValidation dataValidation)
         {
-            dataValidations.Add(dataValidation.Range.RangeAddress.ToString(), dataValidation);
+            dataValidations.Add(dataValidation);
         }
 
         public void Delete(IXLDataValidation dataValidation)
         {
-            dataValidations.Remove(dataValidation.Range.RangeAddress.ToString());
+            dataValidations.RemoveAll(dv=>dv.Ranges.Equals(dataValidation.Ranges));
         }
 
         public IEnumerator<IXLDataValidation> GetEnumerator()
         {
-            return dataValidations.Values.GetEnumerator();
+            return dataValidations.GetEnumerator();
         }
 
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/IXLWorksheet.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/IXLWorksheet.cs
index c4903b0..a8371fc 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/IXLWorksheet.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/IXLWorksheet.cs
@@ -5,6 +5,7 @@
 
 namespace ClosedXML.Excel
 {
+    public enum XLWorksheetVisibility { Visible, Hidden, VeryHidden }
     public interface IXLWorksheet: IXLRangeBase
     {
         /// <summary>
@@ -189,40 +190,40 @@
         /// <summary>
         /// Collapses all outlined rows.
         /// </summary>
-        void CollapseRows();
+        IXLWorksheet CollapseRows();
         /// <summary>
         /// Collapses all outlined columns.
         /// </summary>
-        void CollapseColumns();
+        IXLWorksheet CollapseColumns();
         /// <summary>
         /// Expands all outlined rows.
         /// </summary>
-        void ExpandRows();
+        IXLWorksheet ExpandRows();
         /// <summary>
         /// Expands all outlined columns.
         /// </summary>
-        void ExpandColumns();
+        IXLWorksheet ExpandColumns();
 
         /// <summary>
         /// Collapses the outlined rows of the specified level.
         /// </summary>
         /// <param name="outlineLevel">The outline level.</param>
-        void CollapseRows(Int32 outlineLevel);
+        IXLWorksheet CollapseRows(Int32 outlineLevel);
         /// <summary>
         /// Collapses the outlined columns of the specified level.
         /// </summary>
         /// <param name="outlineLevel">The outline level.</param>
-        void CollapseColumns(Int32 outlineLevel);
+        IXLWorksheet CollapseColumns(Int32 outlineLevel);
         /// <summary>
         /// Expands the outlined rows of the specified level.
         /// </summary>
         /// <param name="outlineLevel">The outline level.</param>
-        void ExpandRows(Int32 outlineLevel);
+        IXLWorksheet ExpandRows(Int32 outlineLevel);
         /// <summary>
         /// Expands the outlined columns of the specified level.
         /// </summary>
         /// <param name="outlineLevel">The outline level.</param>
-        void ExpandColumns(Int32 outlineLevel);
+        IXLWorksheet ExpandColumns(Int32 outlineLevel);
 
         /// <summary>
         /// Deletes this worksheet.
@@ -251,5 +252,9 @@
         IXLRange RangeUsed();
 
         IXLDataValidations DataValidations { get; }
+
+        XLWorksheetVisibility Visibility { get; set; }
+        IXLWorksheet Hide();
+        IXLWorksheet Unhide();
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRangeBase.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRangeBase.cs
index 5ce7046..679a856 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRangeBase.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRangeBase.cs
@@ -141,6 +141,41 @@
         void ClearStyles();
 
         /// <summary>
+        /// Sets the cells' value.
+        /// <para>If the object is an IEnumerable ClosedXML will copy the collection's data into a table starting from each cell.</para>
+        /// <para>If the object is a range ClosedXML will copy the range starting from each cell.</para>
+        /// <para>Setting the value to an object (not IEnumerable/range) will call the object's ToString() method.</para>
+        /// <para>ClosedXML will try to translate it to the corresponding type, if it can't then the value will be left as a string.</para>
+        /// </summary>
+        /// <value>
+        /// The object containing the value(s) to set.
+        /// </value>
+        Object Value { set; }
+
+        /// <summary>
+        /// Sets the type of the cells' data.
+        /// <para>Changing the data type will cause ClosedXML to covert the current value to the new data type.</para>
+        /// <para>An exception will be thrown if the current value cannot be converted to the new data type.</para>
+        /// </summary>
+        /// <value>
+        /// The type of the cell's data.
+        /// </value>
+        /// <exception cref="ArgumentException"></exception>
+        XLCellValues DataType { set; }
+
+        /// <summary>
+        /// Sets the cells' formula with A1 references.
+        /// </summary>
+        /// <value>The formula with A1 references.</value>
+        String FormulaA1 { set; }
+
+        /// <summary>
+        /// Sets the cells' formula with R1C1 references.
+        /// </summary>
+        /// <value>The formula with R1C1 references.</value>
+        String FormulaR1C1 { set; }
+
+        /// <summary>
         /// Converts this object to a range.
         /// </summary>
         IXLRange AsRange();
@@ -158,5 +193,7 @@
         IXLHyperlinks Hyperlinks { get; }
 
         IXLDataValidation DataValidation { get; }
+
+
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs
index 262b6cb..58ca6c7 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/IXLRanges.cs
@@ -22,6 +22,10 @@
         /// <param name="range">The range to remove from this group.</param>
         void Remove(IXLRange range);
 
+        Boolean Contains(IXLRange range);
+
         IXLStyle Style { get; set; }
+
+        IXLDataValidation DataValidation { get; }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs
index c9d225b..2157026 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRange.cs
@@ -29,7 +29,6 @@
             ShiftRows(this.RangeAddress, range, rowsShifted);
         }
 
-
         #region IXLRange Members
 
         public IXLRangeColumn FirstColumn()
@@ -441,5 +440,18 @@
             return new XLTable(this, name, true);
         }
         #endregion
+
+        public override bool Equals(object obj)
+        {
+            var other = (XLRange)obj;
+            return this.RangeAddress.Equals(other.RangeAddress)
+                && this.Worksheet.Equals(other.Worksheet);
+        }
+
+        public override int GetHashCode()
+        {
+            return RangeAddress.GetHashCode()
+                    ^ this.Worksheet.GetHashCode();
+        }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeAddress.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeAddress.cs
index 386d15f..2ae8ce6 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeAddress.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeAddress.cs
@@ -86,5 +86,18 @@
         {
             return firstAddress.ToString() + ":" + lastAddress.ToString();
         }
+
+        public override bool Equals(object obj)
+        {
+            var other = (XLRangeAddress)obj;
+            return this.FirstAddress.Equals(other.FirstAddress)
+                && this.LastAddress.Equals(other.LastAddress);
+        }
+
+        public override int GetHashCode()
+        {
+            return FirstAddress.GetHashCode()
+                    ^ LastAddress.GetHashCode();
+        }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs
index 5c6d45d..b1aeb6a 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRangeBase.cs
@@ -893,40 +893,56 @@
             get 
             {
                 String address = this.RangeAddress.ToString();
-                if (Worksheet.DataValidations.Where(dv => dv.Range.RangeAddress.ToString() == address).Any())
+                if (Worksheet.DataValidations.Where(dv => 
+                    dv.Ranges.Count() == 1
+                    && dv.Ranges.Contains(this.AsRange())
+                    ).Any())
                 {
-                    return Worksheet.DataValidations.Where(dv => dv.Range.RangeAddress.ToString() == address).Single();
+                    return Worksheet.DataValidations.Where(dv => dv.Ranges.Contains(this.AsRange())).Single();
                 }
                 else
                 {
-                    var dv = DataValidationsIntersects();
-                    if (dv != null)
+                    foreach (var dv in Worksheet.DataValidations)
                     {
-                        dv.Delete();
-                        foreach (var c in dv.Range.Cells())
+                        foreach (var dvRange in dv.Ranges)
                         {
-                            if (!this.Contains(c.Address.ToString()))
+                            if (dvRange.Intersects(this))
                             {
-                                c.DataValidation.CopyFrom(dv);
+                                dv.Ranges.Remove(dvRange);
+                                foreach (var c in dvRange.Cells())
+                                {
+                                    if (!this.Contains(c.Address.ToString()))
+                                        dv.Ranges.Add(c.AsRange());
+                                }
                             }
                         }
                     }
 
-                    var dataValidation = new XLDataValidation(this.AsRange());
+                    var newRanges = new XLRanges(Worksheet.Internals.Workbook, Style);
+                    newRanges.Add(this.AsRange());
+                    var dataValidation = new XLDataValidation(newRanges, Worksheet);
+                    
                     Worksheet.DataValidations.Add(dataValidation);
                     return dataValidation;
                 }
             }
         }
 
-        private IXLDataValidation DataValidationsIntersects()
+        public Object Value
         {
-            foreach (var dv in Worksheet.DataValidations)
+            set
             {
-                if (dv.Range.Intersects(this))
-                    return dv;
+                Cells().ForEach(c => c.Value = value);
             }
-            return null;
         }
+
+        public XLCellValues DataType
+        {
+            set
+            {
+                Cells().ForEach(c => c.DataType = value);
+            }
+        }
+
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs
index 2c85a9f..b7eeb39 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Ranges/XLRanges.cs
@@ -109,6 +109,83 @@
             return retVal;
         }
 
+        public override bool Equals(object obj)
+        {
+            var other = (XLRanges)obj;
 
+            if (this.ranges.Count != other.ranges.Count)
+            {
+                return false;
+            }
+            else
+            {
+                foreach (var thisRange in this.ranges)
+                {
+                    Boolean foundOne = false;
+                    foreach (var otherRange in other.ranges)
+                    {
+                        if (thisRange.Equals(otherRange))
+                        {
+                            foundOne = true;
+                            break;
+                        }
+                    }
+
+                    if (!foundOne)
+                        return false;
+                }
+
+                return true;
+            }
+        }
+
+        public Boolean Contains(IXLRange range)
+        {
+            foreach (var r in this.ranges)
+            {
+                if (r.Equals(range)) return true;
+            }
+            return false;
+        }
+
+        public override int GetHashCode()
+        {
+            Int32 hash = 0;
+            foreach (var r in this.ranges)
+            {
+                hash ^= r.GetHashCode();
+            }
+            return hash;
+        }
+
+        public IXLDataValidation DataValidation
+        {
+            get
+            {
+                foreach (var range in ranges)
+                {
+                    String address = range.RangeAddress.ToString();
+                    foreach (var dv in range.Worksheet.DataValidations)
+                    {
+                        foreach (var dvRange in dv.Ranges)
+                        {
+                            if (dvRange.Intersects(range))
+                            {
+                                dv.Ranges.Remove(dvRange);
+                                foreach (var c in dvRange.Cells())
+                                {
+                                    if (!range.Contains(c.Address.ToString()))
+                                        dv.Ranges.Add(c.AsRange());
+                                }
+                            }
+                        }
+                    }
+                }
+                var dataValidation = new XLDataValidation(this, ranges.First().Worksheet);
+
+                ranges.First().Worksheet.DataValidations.Add(dataValidation);
+                return dataValidation;
+            }
+        }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs
index aa266ec..03b31d0 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLAddress.cs
@@ -122,9 +122,9 @@
             {
                 Boolean retVal = true;
                 String theColumn = column.ToUpper();
-                for (Int32 i = 1; i <= column.Length; i++)
+                for (Int32 i = 0; i < column.Length; i++)
                 {
-                    if (theColumn[i] < 'A' || theColumn[i] > 'Z' || (i == 3 && theColumn[i] > 'D'))
+                    if (theColumn[i] < 'A' || theColumn[i] > 'Z' || (i == 2 && theColumn[i] > 'D'))
                     {
                         retVal = false;
                         break;
@@ -134,6 +134,29 @@
             }
         }
 
+        public static Boolean IsValidRow(String rowString)
+        {
+            Int32 row;
+            if (Int32.TryParse(rowString, out row))
+                return row > 0 && row <= XLWorksheet.MaxNumberOfRows;
+            else
+                return false;
+        }
+
+        public static Boolean IsValidA1Address(String address)
+        {
+            address = address.Replace("$", "");
+            Int32 rowPos = 0;
+            while (rowPos < address.Length && (address[rowPos] > '9' || address[rowPos] < '0'))
+                rowPos++;
+
+            return 
+                   rowPos < address.Length
+                && IsValidRow(address.Substring(rowPos))
+                && IsValidColumn(address.Substring(0, rowPos));
+        }
+
+
         /// <summary>
         /// Gets the column letter of a given column number.
         /// </summary>
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs
index 716d107..1013d87 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs
@@ -109,6 +109,10 @@
 
                 var ws = (XLWorksheet)Worksheets.Add(sheetName);
                 ws.RelId = dSheet.Id;
+
+                if (dSheet.State != null)
+                    ws.Visibility = sheetStateValues.Single(p => p.Value == dSheet.State).Key;
+
                 var sheetFormatProperties = (SheetFormatProperties)worksheetPart.Worksheet.Descendants<SheetFormatProperties>().First();
                 if (sheetFormatProperties.DefaultRowHeight != null)
                     ws.RowHeight = sheetFormatProperties.DefaultRowHeight;
@@ -407,21 +411,23 @@
                 var dataValidations = (DataValidations)dataValidationList.First();
                 foreach (var dvs in dataValidations.Descendants<DataValidation>())
                 {
-                    var dvt = ws.Range(dvs.SequenceOfReferences.InnerText).DataValidation;
-                    if (dvs.AllowBlank != null) dvt.IgnoreBlanks = dvs.AllowBlank;
-                    if (dvs.ShowDropDown != null) dvt.InCellDropdown = !dvs.ShowDropDown.Value;
-                    if (dvs.ShowErrorMessage != null) dvt.ShowErrorMessage = dvs.ShowErrorMessage;
-                    if (dvs.ShowInputMessage != null) dvt.ShowInputMessage = dvs.ShowInputMessage;
-                    if (dvs.PromptTitle != null) dvt.InputTitle = dvs.PromptTitle;
-                    if (dvs.Prompt != null) dvt.InputMessage = dvs.Prompt;
-                    if (dvs.ErrorTitle != null) dvt.ErrorTitle = dvs.ErrorTitle;
-                    if (dvs.Error != null) dvt.ErrorMessage = dvs.Error;
-                    if (dvs.ErrorStyle != null) dvt.ErrorStyle = dataValidationErrorStyleValues.Single(p => p.Value == dvs.ErrorStyle).Key;
-                    if (dvs.Type != null) dvt.AllowedValues = dataValidationValues.Single(p => p.Value == dvs.Type).Key;
-                    if (dvs.Operator != null) dvt.Operator = dataValidationOperatorValues.Single(p => p.Value == dvs.Operator).Key;
-                    if (dvs.Formula1 != null) dvt.MinValue = dvs.Formula1.Text;
-                    if (dvs.Formula2 != null) dvt.MaxValue = dvs.Formula2.Text;
-
+                    foreach (String rangeAddress in dvs.SequenceOfReferences.InnerText.Split(' '))
+                    {
+                        var dvt = ws.Range(rangeAddress).DataValidation;
+                        if (dvs.AllowBlank != null) dvt.IgnoreBlanks = dvs.AllowBlank;
+                        if (dvs.ShowDropDown != null) dvt.InCellDropdown = !dvs.ShowDropDown.Value;
+                        if (dvs.ShowErrorMessage != null) dvt.ShowErrorMessage = dvs.ShowErrorMessage;
+                        if (dvs.ShowInputMessage != null) dvt.ShowInputMessage = dvs.ShowInputMessage;
+                        if (dvs.PromptTitle != null) dvt.InputTitle = dvs.PromptTitle;
+                        if (dvs.Prompt != null) dvt.InputMessage = dvs.Prompt;
+                        if (dvs.ErrorTitle != null) dvt.ErrorTitle = dvs.ErrorTitle;
+                        if (dvs.Error != null) dvt.ErrorMessage = dvs.Error;
+                        if (dvs.ErrorStyle != null) dvt.ErrorStyle = dataValidationErrorStyleValues.Single(p => p.Value == dvs.ErrorStyle).Key;
+                        if (dvs.Type != null) dvt.AllowedValues = dataValidationValues.Single(p => p.Value == dvs.Type).Key;
+                        if (dvs.Operator != null) dvt.Operator = dataValidationOperatorValues.Single(p => p.Value == dvs.Operator).Key;
+                        if (dvs.Formula1 != null) dvt.MinValue = dvs.Formula1.Text;
+                        if (dvs.Formula2 != null) dvt.MaxValue = dvs.Formula2.Text;
+                    }
                 }
             }
         }
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
index 88ad821..69b6b9e 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
@@ -37,6 +37,7 @@
         private List<KeyValuePair<XLAllowedValues, DataValidationValues>> dataValidationValues = new List<KeyValuePair<XLAllowedValues, DataValidationValues>>();
         private List<KeyValuePair<XLErrorStyle, DataValidationErrorStyleValues>> dataValidationErrorStyleValues = new List<KeyValuePair<XLErrorStyle, DataValidationErrorStyleValues>>();
         private List<KeyValuePair<XLOperator, DataValidationOperatorValues>> dataValidationOperatorValues = new List<KeyValuePair<XLOperator, DataValidationOperatorValues>>();
+        private List<KeyValuePair<XLWorksheetVisibility, SheetStateValues>> sheetStateValues = new List<KeyValuePair<XLWorksheetVisibility, SheetStateValues>>();
 
         private Boolean populated = false;
         private void PopulateEnums()
@@ -60,6 +61,7 @@
                 PopulateDataValidationValues();
                 PopulateDataValidationErrorStyleValues();
                 PopulateDataValidationOperatorValues();
+                PopulateSheetStateValues();
                 populated = true;
             }
         }
@@ -307,6 +309,13 @@
             dataValidationOperatorValues.Add(new KeyValuePair<XLOperator, DataValidationOperatorValues>(XLOperator.NotEqualTo, DataValidationOperatorValues.NotEqual));
         }
 
+        private void PopulateSheetStateValues()
+        {
+            sheetStateValues.Add(new KeyValuePair<XLWorksheetVisibility, SheetStateValues>(XLWorksheetVisibility.Visible, SheetStateValues.Visible));
+            sheetStateValues.Add(new KeyValuePair<XLWorksheetVisibility, SheetStateValues>(XLWorksheetVisibility.Hidden, SheetStateValues.Hidden));
+            sheetStateValues.Add(new KeyValuePair<XLWorksheetVisibility, SheetStateValues>(XLWorksheetVisibility.VeryHidden, SheetStateValues.VeryHidden));
+        }
+
         #endregion
 
         private void CreatePackage(String filePath)
@@ -641,7 +650,17 @@
 
                 xlSheet.SheetId = Int32.Parse(rId.Substring(3));
                 xlSheet.RelId = rId;
-                workbook.Sheets.Append(new Sheet() { Name = xlSheet.Name, Id = rId, SheetId = (UInt32)xlSheet.SheetId });
+                var newSheet = new Sheet()
+                {
+                    Name = xlSheet.Name,
+                    Id = rId,
+                    SheetId = (UInt32)xlSheet.SheetId
+                };
+                
+                if (xlSheet.Visibility != XLWorksheetVisibility.Visible)
+                    newSheet.State = sheetStateValues.Single(p => p.Key == xlSheet.Visibility).Value;
+
+                workbook.Sheets.Append(newSheet);
             }
 
             var sheetElements = from sheet in workbook.Sheets.Elements<Sheet>()
@@ -1985,6 +2004,13 @@
                 dataValidations.RemoveAllChildren<DataValidation>();
                 foreach (var dv in xlWorksheet.DataValidations)
                 {
+                    String sequence = String.Empty;
+                    foreach (var r in dv.Ranges)
+                    {
+                        sequence += r.RangeAddress.ToString() + " ";
+                    }
+                    sequence = sequence.Substring(0, sequence.Length - 1);
+
                     DataValidation dataValidation = new DataValidation()
                     {
                         AllowBlank = dv.IgnoreBlanks,
@@ -2000,7 +2026,7 @@
                         ShowInputMessage = dv.ShowInputMessage,
                         ErrorStyle = dataValidationErrorStyleValues.Single(p => p.Key == dv.ErrorStyle).Value,
                         Operator = dataValidationOperatorValues.Single(p => p.Key == dv.Operator).Value,
-                        SequenceOfReferences = new ListValue<StringValue>() { InnerText = dv.Range.RangeAddress.ToString() }
+                        SequenceOfReferences = new ListValue<StringValue>() { InnerText = sequence }
                     };
                     
                     dataValidations.Append(dataValidation);
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
index b96268f..676c0ae 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorksheet.cs
@@ -443,50 +443,58 @@
             return Range(1, 1, XLWorksheet.MaxNumberOfRows, XLWorksheet.MaxNumberOfColumns);
         }
 
-        public void CollapseRows()
+        public IXLWorksheet CollapseRows()
         {
             Enumerable.Range(1, 8).ForEach(i => CollapseRows(i));
+            return this;
         }
-        public void CollapseColumns()
+        public IXLWorksheet CollapseColumns()
         {
             Enumerable.Range(1, 8).ForEach(i => CollapseColumns(i));
+            return this;
         }
-        public void ExpandRows()
+        public IXLWorksheet ExpandRows()
         {
             Enumerable.Range(1, 8).ForEach(i => ExpandRows(i));
+            return this;
         }
-        public void ExpandColumns()
+        public IXLWorksheet ExpandColumns()
         {
             Enumerable.Range(1, 8).ForEach(i => ExpandRows(i));
+            return this;
         }
-
-        public void CollapseRows(Int32 outlineLevel)
+               
+        public IXLWorksheet CollapseRows(Int32 outlineLevel)
         {
             if (outlineLevel < 1 || outlineLevel > 8)
                 throw new ArgumentOutOfRangeException("Outline level must be between 1 and 8.");
 
             Internals.RowsCollection.Values.Where(r => r.OutlineLevel == outlineLevel).ForEach(r => r.Collapse());
+            return this;
         }
-        public void CollapseColumns(Int32 outlineLevel)
+        public IXLWorksheet CollapseColumns(Int32 outlineLevel)
         {
             if (outlineLevel < 1 || outlineLevel > 8)
                 throw new ArgumentOutOfRangeException("Outline level must be between 1 and 8.");
 
             Internals.ColumnsCollection.Values.Where(c => c.OutlineLevel == outlineLevel).ForEach(c => c.Collapse());
+            return this;
         }
-        public void ExpandRows(Int32 outlineLevel)
+        public IXLWorksheet ExpandRows(Int32 outlineLevel)
         {
             if (outlineLevel < 1 || outlineLevel > 8)
                 throw new ArgumentOutOfRangeException("Outline level must be between 1 and 8.");
 
             Internals.RowsCollection.Values.Where(r => r.OutlineLevel == outlineLevel).ForEach(r => r.Expand());
+            return this;
         }
-        public void ExpandColumns(Int32 outlineLevel)
+        public IXLWorksheet ExpandColumns(Int32 outlineLevel)
         {
             if (outlineLevel < 1 || outlineLevel > 8)
                 throw new ArgumentOutOfRangeException("Outline level must be between 1 and 8.");
 
             Internals.ColumnsCollection.Values.Where(c => c.OutlineLevel == outlineLevel).ForEach(c => c.Expand());
+            return this;
         }
 
         public void Delete()
@@ -602,5 +610,18 @@
 
         public new IXLHyperlinks Hyperlinks { get; private set; }
         public IXLDataValidations DataValidations { get; private set; }
+
+        public XLWorksheetVisibility Visibility { get; set; }
+        public IXLWorksheet Hide()
+        {
+            Visibility = XLWorksheetVisibility.Hidden;
+            return this;
+        }
+        public IXLWorksheet Unhide()
+        {
+            Visibility = XLWorksheetVisibility.Visible;
+            return this;
+        }
+
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML_Examples/ClosedXML_Examples.csproj b/ClosedXML/ClosedXML/ClosedXML_Examples/ClosedXML_Examples.csproj
index b62fc6d..fd152ab 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Examples/ClosedXML_Examples.csproj
+++ b/ClosedXML/ClosedXML/ClosedXML_Examples/ClosedXML_Examples.csproj
@@ -89,6 +89,7 @@
     <Compile Include="Misc\AdjustToContents.cs" />
     <Compile Include="Misc\Collections.cs" />
     <Compile Include="Misc\BlankCells.cs" />
+    <Compile Include="Misc\HideSheets.cs" />
     <Compile Include="Misc\DataValidation.cs" />
     <Compile Include="Misc\Hyperlinks.cs" />
     <Compile Include="Misc\InsertingData.cs" />
diff --git a/ClosedXML/ClosedXML/ClosedXML_Examples/Creating/CreateFiles.cs b/ClosedXML/ClosedXML/ClosedXML_Examples/Creating/CreateFiles.cs
index 61a8bfb..1032a19 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Examples/Creating/CreateFiles.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Examples/Creating/CreateFiles.cs
@@ -70,6 +70,7 @@
             new InsertingData().Create(@"C:\Excel Files\Created\InsertingData.xlsx");
             new Hyperlinks().Create(@"C:\Excel Files\Created\Hyperlinks.xlsx");
             new DataValidation().Create(@"C:\Excel Files\Created\DataValidation.xlsx");
+            new HideSheets().Create(@"C:\Excel Files\Created\HideSheets.xlsx");
         }
     }
 }
diff --git a/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/DataValidation.cs b/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/DataValidation.cs
index 2bc0e93..4ecb1e0 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/DataValidation.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/DataValidation.cs
@@ -76,6 +76,21 @@
             ws.Range("B1:B4").DataValidation.WholeNumber.EqualTo(1);
             ws.Range("B3:B4").DataValidation.WholeNumber.EqualTo(2);
 
+
+            // Validate with multiple ranges
+            var ws2 = wb.Worksheets.Add("Validate Ranges");
+            var rng1Validation = ws2.Ranges("A1:B2,B4:D7,F4:G5").DataValidation;
+            rng1Validation.Decimal.EqualTo(1);
+            rng1Validation.IgnoreBlanks = false;
+
+            var rng2Validation = ws2.Range("A11:E14").DataValidation;
+            rng2Validation.Decimal.EqualTo(2);
+            rng2Validation.IgnoreBlanks = false;
+
+            var rng3Validation = ws2.Range("B2:B12").DataValidation;
+            rng3Validation.Decimal.EqualTo(3);
+            rng3Validation.IgnoreBlanks = true;
+
             wb.SaveAs(filePath);
         }
 
diff --git a/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/HideSheets.cs b/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/HideSheets.cs
new file mode 100644
index 0000000..25c3bfd
--- /dev/null
+++ b/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/HideSheets.cs
@@ -0,0 +1,66 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using ClosedXML.Excel;
+
+using System.Drawing;
+
+namespace ClosedXML_Examples.Misc
+{
+    public class HideSheets
+    {
+        #region Variables
+
+        // Public
+
+        // Private
+
+
+        #endregion
+
+        #region Properties
+
+        // Public
+
+        // Private
+
+        // Override
+
+
+        #endregion
+
+        #region Events
+
+        // Public
+
+        // Private
+
+        // Override
+
+
+        #endregion
+
+        #region Methods
+
+        // Public
+        public void Create(String filePath)
+        {
+            var wb = new XLWorkbook();
+
+            wb.Worksheets.Add("Visible");
+            wb.Worksheets.Add("Hidden").Hide();
+            wb.Worksheets.Add("Unhidden").Hide().Unhide();
+            wb.Worksheets.Add("VeryHidden").Visibility = XLWorksheetVisibility.VeryHidden;
+
+            wb.SaveAs(filePath);
+        }
+
+        // Private
+
+        // Override
+
+
+        #endregion
+    }
+}
diff --git a/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/HideUnhide.cs b/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/HideUnhide.cs
index 274aab3..a43a0b2 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/HideUnhide.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Examples/Misc/HideUnhide.cs
@@ -47,7 +47,7 @@
         public void Create(String filePath)
         {
             var wb = new XLWorkbook();
-            var ws = wb.Worksheets.Add("Hide Unhide");
+            var ws = wb.Worksheets.Add("Hide Rows Columns");
 
             ws.Columns(1, 3).Hide();
             ws.Rows(1, 3).Hide();
diff --git a/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs b/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs
index 6ae10c6..427b44a 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Sandbox/Program.cs
@@ -16,9 +16,14 @@
         static void Main(string[] args)
         {
             //var fileName = "Issue_6266";
-            var fileName = "Issue_6257";
-            var wb = new XLWorkbook(String.Format(@"c:\Excel Files\ForTesting\{0}.xlsx", fileName));
-
+            //var fileName = "Issue_6257";
+            var fileName = "Sandbox";
+            //var wb = new XLWorkbook(String.Format(@"c:\Excel Files\ForTesting\{0}.xlsx", fileName));
+            var wb = new XLWorkbook();
+            var ws = wb.Worksheets.Add("New");
+            ws.Range("A1:B1").Value = "X";
+            ws.Cell(1, 1).AsRange().InsertRowsAbove(1);
+            
 
             wb.SaveAs(String.Format(@"c:\Excel Files\ForTesting\{0}_Saved.xlsx", fileName));
         }
@@ -91,23 +96,42 @@
             List<Double> runningLoad = new List<Double>();
             List<Double> runningSavedBack = new List<Double>();
             
-            foreach (Int32 r in Enumerable.Range(1, 5))
+            foreach (Int32 r in Enumerable.Range(1, 1))
             {
                 var wb = new XLWorkbook();
                 var startTotal = DateTime.Now;
                 foreach (var i in Enumerable.Range(1, 1))
                 {
                     var ws = wb.Worksheets.Add("Sheet" + i);
-                    foreach (var ro in Enumerable.Range(1, 2000))
+                    foreach (var ro in Enumerable.Range(1, 50))
                     {
-                        foreach (var co in Enumerable.Range(1, 100))
+                        foreach (var co in Enumerable.Range(1, 50))
                         {
                             ws.Cell(ro, co).Style = GetRandomStyle();
                             ws.Cell(ro, co).Value = GetRandomValue();
                         }
                         //System.Threading.Thread.Sleep(10);
                     }
+                    ws.RangeUsed().Style.Border.BottomBorder = XLBorderStyleValues.DashDot;
+                    ws.RangeUsed().Style.Border.BottomBorderColor = XLColor.AirForceBlue;
+                    ws.RangeUsed().Style.Border.TopBorder = XLBorderStyleValues.DashDotDot;
+                    ws.RangeUsed().Style.Border.TopBorderColor = XLColor.AliceBlue;
+                    ws.RangeUsed().Style.Border.LeftBorder = XLBorderStyleValues.Dashed;
+                    ws.RangeUsed().Style.Border.LeftBorderColor = XLColor.Alizarin;
+                    ws.RangeUsed().Style.Border.RightBorder = XLBorderStyleValues.Dotted;
+                    ws.RangeUsed().Style.Border.RightBorderColor = XLColor.Almond;
+
+                    ws.RangeUsed().Style.Font.Bold = true;
+                    ws.RangeUsed().Style.Font.FontColor = XLColor.Amaranth;
+                    ws.RangeUsed().Style.Font.FontSize = 10;
+                    ws.RangeUsed().Style.Font.Italic = true;
+
+                    ws.RangeUsed().Style.Alignment.Horizontal = XLAlignmentHorizontalValues.Center;
+                    ws.RangeUsed().Style.Alignment.Vertical = XLAlignmentVerticalValues.Center;
+                    ws.RangeUsed().Style.Alignment.WrapText = true;
                 }
+
+
                 //var start3 = DateTime.Now;
                 //foreach (var ws in wb.Worksheets)
                 //{