This would allow repeating header rows on every printed page. More information related to this functionality may be found on the following link:

https://support.office.com/en-us/article/Print-rows-with-column-headers-on-top-of-every-page-d3550133-f6a1-4c72-ad70-5309a2e8fe8c

Incorrectly resolved fill between local formatting and cell style.

A fill (fillId) of a cell style (cellStyleXfs) is respected instead of the fill (fillId) of the local formatting (cellXfs).

Currently, the numbers in a CSV file are parsed as numbers, and the leading zeros are lost. In MS Excel, leading zeros could be preserved when the values are imported as text using the more sophisticated text import wizard (http://www.upenn.edu/computing/da/bo/webi/qna/iv_csvLeadingZeros.html ).

Workaround: The values could be extracted using a third-party (or custom) CSV parser, and inserted manually into the model, using CellSelection.SetValueAsText method (http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/working-with-cells/cell-value-types.html ).

Use the below code snippet to generate XLSX document and export it. You will notice that the export operation is extremely slow:

Stopwatch sw = new Stopwatch();
sw.Start();
IWorkbookFormatProvider formatProvider = new Telerik.Windows.Documents.Spreadsheet.FormatProviders.OpenXml.Xlsx.XlsxFormatProvider();
Workbook workbook = new Workbook();
Worksheet worksheet = workbook.Worksheets.Add();
Worksheet worksheet2 = workbook.Worksheets.Add();
worksheet2.Name ="Days";
List<string> weekdays = new List<string>() { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
for (int i = 0; i < 7; i++)
{
    worksheet2.Cells[0, i].SetValue(weekdays[i]);
}

for (int i = 0; i < 200; i++)
{
    for (int j = 0; j < 10; j++)
    {

        CellIndex cellIndex = new CellIndex(i, j);
        CellSelection selection = worksheet.Cells[cellIndex];
        selection.SetValue("Wednesday");

        var context = new ListDataValidationRuleContext(worksheet, cellIndex)
        {
            InputMessageTitle = "InputMessageTitle",
            InputMessageContent = "InputMessageTitle"
        };

        context.ErrorStyle = ErrorStyle.Stop;
        context.ErrorAlertTitle = "ErrorAlertTitle";
        context.ErrorAlertContent = "ErrorAlertContent";
        context.InCellDropdown = true;
        context.Argument1 = "=Days!A0:A6"; //"Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday";
        ListDataValidationRule rule = new(context);
        worksheet.Cells[cellIndex].SetDataValidationRule(rule);
    }
}

string outputFile = @"..\..\..\output.xlsx";
File.Delete(outputFile);

using (Stream output = new FileStream(outputFile, FileMode.Create))
{

    formatProvider.Export(workbook, output);
}
sw.Stop();
Debug.WriteLine("Export " + sw.ElapsedMilliseconds);

Add support for creating Tables and applying tables styles (predefined ones or custom).

Import an XLSX document and auto-fit the columns. Then, export the document to XLSX format.

Even though a SpreadFixedTextMeasurer is applied and a FontProvider is implemented, the columns are not wide enough to fit the content:

XIRR function returns the internal rate of return for a schedule of cash flows that is not necessarily periodic. To calculate the internal rate of return for a series of periodic cash flows, use the IRR function.

https://support.microsoft.com/en-gb/office/xirr-function-de1242ec-6477-445b-b11b-a303ad9adc9d 

The charts have a display blanks as property which is represented by the dispBlanksAs element. The absence of this element sometimes makes drastic difference in the way a chart might look. E.g. the following chart has a gap in its data and depending on what value dispBlanksAs has, it looks very different.

Incorrect calculation of UsedCellRange when conditional formatting is applied to a large cell range.

Workaround:

var usedCellRange = workbook.ActiveWorksheet.GetUsedCellRange(
    CellPropertyDefinitions.AllPropertyDefinitions
    .Except(
        CellPropertyDefinitions.AllPropertyDefinitions.Where(p => p.Name == "DataValidationRule" || p.Name == "ConditionalFormatting")));