// TODO: Hyperlink cell range
        /// <summary>
        /// Insert a hyperlink.
        /// </summary>
        /// <param name="RowIndex">The row index.</param>
        /// <param name="ColumnIndex">The column index.</param>
        /// <param name="HyperlinkType">The type of hyperlink.</param>
        /// <param name="Address">The URL for web pages, the file path for existing files, a cell reference (such as Sheet1!A1 or Sheet1!A1:B5), a defined name or an email address. NOTE: Do NOT include the "mailto:" portion for email addresses.</param>
        /// <param name="Display">The display text. Set null or an empty string to use the default.</param>
        /// <param name="ToolTip">The tooltip (or screentip) text. Set null or an empty string to ignore this.</param>
        /// <param name="OverwriteExistingCell">True to overwrite the existing cell value with the hyperlink display text. False otherwise.</param>
        /// <returns>True if successful. False otherwise.</returns>
        public bool InsertHyperlink(int RowIndex, int ColumnIndex, SLHyperlinkTypeValues HyperlinkType, string Address, string Display, string ToolTip, bool OverwriteExistingCell)
        {
            if (RowIndex < 1 || RowIndex > SLConstants.RowLimit) return false;
            if (ColumnIndex < 1 || ColumnIndex > SLConstants.ColumnLimit) return false;

            SLHyperlink hl = new SLHyperlink();
            hl.IsNew = true;

            hl.Reference = new SLCellPointRange(RowIndex, ColumnIndex, RowIndex, ColumnIndex);

            switch (HyperlinkType)
            {
                case SLHyperlinkTypeValues.EmailAddress:
                    hl.IsExternal = true;
                    hl.HyperlinkUri = string.Format("mailto:{0}", Address);
                    hl.HyperlinkUriKind = UriKind.Absolute;
                    break;
                case SLHyperlinkTypeValues.FilePath:
                    hl.IsExternal = true;
                    hl.HyperlinkUri = Address;
                    // assume if it starts with ../ or ./ it's a relative path.
                    hl.HyperlinkUriKind = Address.StartsWith(".") ? UriKind.Relative : UriKind.Absolute;
                    break;
                case SLHyperlinkTypeValues.InternalDocumentLink:
                    hl.IsExternal = false;
                    hl.Location = Address;
                    break;
                case SLHyperlinkTypeValues.Url:
                    hl.IsExternal = true;
                    hl.HyperlinkUri = Address;
                    hl.HyperlinkUriKind = UriKind.Absolute;
                    break;
            }

            if (Display == null)
            {
                hl.Display = Address;
            }
            else
            {
                if (Display.Length == 0)
                {
                    hl.Display = Address;
                }
                else
                {
                    hl.Display = Display;
                }
            }

            if (ToolTip != null && ToolTip.Length > 0) hl.ToolTip = ToolTip;

            SLCellPoint pt = new SLCellPoint(RowIndex, ColumnIndex);
            SLCell c;
            SLStyle style;
            if (slws.Cells.ContainsKey(pt))
            {
                c = slws.Cells[pt];
                style = new SLStyle();
                if (c.StyleIndex < listStyle.Count) style.FromHash(listStyle[(int)c.StyleIndex]);
                else style.FromHash(listStyle[0]);
                style.SetFontUnderline(UnderlineValues.Single);
                style.SetFontColor(SLThemeColorIndexValues.Hyperlink);
                c.StyleIndex = (uint)this.SaveToStylesheet(style.ToHash());

                if (OverwriteExistingCell)
                {
                    // in case there's a formula
                    c.CellFormula = null;
                    c.DataType = CellValues.SharedString;
                    c.CellText = this.DirectSaveToSharedStringTable(hl.Display).ToString(CultureInfo.InvariantCulture);
                }
                // else don't have to do anything

                slws.Cells[pt] = c.Clone();
            }
            else
            {
                c = new SLCell();

                style = new SLStyle();
                style.FromHash(listStyle[0]);
                style.SetFontUnderline(UnderlineValues.Single);
                style.SetFontColor(SLThemeColorIndexValues.Hyperlink);
                c.StyleIndex = (uint)this.SaveToStylesheet(style.ToHash());

                c.DataType = CellValues.SharedString;
                c.CellText = this.DirectSaveToSharedStringTable(hl.Display).ToString(CultureInfo.InvariantCulture);
                slws.Cells[pt] = c.Clone();
            }

            slws.Hyperlinks.Add(hl);

            return true;
        }