Some functions are exported from Excel with the _xlfn. prefix as compatibility measure with older versions of MS Excel (future functions, see here https://msdn.microsoft.com/en-us/library/dd907480(v=office.12).aspx , https://support.office.com/en-ca/article/Issue-An-xlfn-prefix-is-displayed-in-front-of-a-formula-882f1ef7-68fb-4fcd-8d54-9fbb77fd5025 )

RadSpreadProcessing do not support these and the spreadsheet treats the function as not supported even when it is.

Example:

    <row r="1" spans="2:2" x14ac:dyDescent="0.25">
      <c r="B1" t="b">
        <f>_xlfn.ISFORMULA(C2)</f>
        <v>0</v>
      </c>
    </row>


This could be observed with the ISFORMULA function.

At this point the culture used by RadSpreadProcessing (in the FormatHelper and internally in SpreadsheetCultureHelper) is determined by the current thread culture on startup. Provide ability to:
- to change the culture at runtime. Currently, when the thread culture is changed, RadSpreadProcessing is "stuck" with the original one.
- set this culture independently of the current thread's one.

Implement export to XPS file format.

Add support for MID function. MID returns a specific number of characters from a text string, starting at the position you specify, based on the number of characters you specify.

MID(text, start_num, num_chars)

A list of the supported functions is available at http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/functions

This function can be implemented as a custom function. Check the following resources for more details on how to achieve that:

- http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions
- https://github.com/telerik/xaml-sdk/tree/master/Spreadsheet/WPF/CustomFunctions

Add support for ROW function: https://support.office.com/en-us/article/ROW-function-3a63b74a-c4d0-4093-b49a-e76eb49a6d8d?ui=en-US&rs=en-US&ad=US

Examples:

=ROW() returns the row in which the formula appears
=ROW(C10) returns the row of the reference - 10


Workaround: This could be implemented as a custom function: http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions.html

If shape extent is declared, the two cell anchor points for the drawing element are ignored. For example if the TwoCellAnchorElement's from and two points declare that the image should be anchored starting from cell A1to F10 and further in the drawing declaration there is defined extents element with image size values, anchor element's points are ignored. 

The r attribute of a cell defines the reference the cell is pointing to in a style similar to A1. Setting this attribute is optional but when set to an empty string, it cannot be imported - an ArgumentException is thrown with message "cellName" by the Guard class in NameConverter.ConvertCellNameToIndex().

Here is an example of such a definition:

<row r="1" spans="1:12">
  <c r=""/>
</row>


MS Excel and Libre Office can open such documents.

Having cell with custom format string set to "MMM" does not apply correctly. Instead of showing the date in the defined format (for instance "Aug"), what actually is displayed is "MMM".

The OFFSET function returns a reference to a range that is a specified number of rows and columns from a cell or range of cells. 

When the scale factor of a document is smaller, the borders don't seem to scale correctly when exported to PDF. They appear much thicker than they would when exported from Excel.

When inserting cells a check is performed for data loss. This check should take into account the value property, but should not take into account properties like cell value format and data validation. 

Workaround: clear the values at the end of the worksheet before inserting cells.
worksheet.Cells[1048575, 0, 1048575, 16383].ClearDataValidationRule();

Add support for Point Markes customization options for the Charts.

Exporting empty workbook without any worksheet is not allowed according to the specification and such documents cannot be opened in Excel. Ensure the customers cannot create such documents using the API of SpreadProcessing.

Currently, row/column groups cannot be collapsed/expanded through the public API. User should be able to specify row's/column's "collapsed" attribute indicating whether the outlining is in a collapsed state.

Currently, the worksheet of the shape and the collection it belongs to should be the same. Make it possible for the ChartShape and the data source to be on different worksheets.

Adding a formula with the SetValueAsFormula method is slow

Currently, this could be achieved by exporting the document to PDF and then by using RadPdfViewer's WPF control ThumbnailFactory class. Sample code may be seen at this forum post: http://www.telerik.com/forums/pdf-thumbnail-returns-transparent-images#jO33X-E8Cki_qLh_KsToWg Help article: WPF PdfViewer - Exporting Fixed Page to Image - Telerik UI for WPF