The SUMIFS function adds all of its arguments that meet multiple criteria.

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

Handle the case when the cell is too small and the value contains a decimal separator. 

For example, see attached images. 

Currently, if you have a cell that merges into multiple columns, when you click on the column header, this will select also the adjacent columns where the merged cell extends. Add an option to disable this functionality and select only the cells in the clicked column.

Add the CellIndex or CellRange of the clicked cell in the HyperlinkClicked event arguments (HyperlinkClickedEventArgs).

Currently, the HyperlinkClicked event of RadWorksheetEditor is raised only for external hyperlinks (web and mailto addresses). Raise the event also for links pointing to the a cell in the same document.

Returns a Range object that represents the current region. The current region is a range bounded by any combination of blank rows and blank columns. If we want to be consistent with MS Excel we should implement this property. It is useful for many operations of a region such as filtering(selecting one cell and executing the Filter command should apply it to the current region), sorting, selecting all and etc. This document will be useful: https://docs.microsoft.com/en-us/office/vba/api/excel.range.currentregion.

Introduce support for sorting columns that contain merged cells. 

Add support for text orientation (rotation). This is supported in the SpreadProcessing model.

Currently, the insert hyperlink dialog displayed on Ctrl+K press in the selected cell (or cell range) allows you to create a link to a webpage page, email address or place in the same document. 

Add a "Create New Document" option that allows you to create a document from the selected cell range, like in the Excel version of the Insert Hyperlink dialog. 

Add information about the selection in the SelectionChanged event arguments. 

- We need to differentiate from mouse event to keyboard event. But since the EventArgs is empty we are not able to differentiate.

Add an event that indicates when a hyperlink is clicked.

Spreadsheet: Add the ability to build formulas using keyboard navigation:

1. Press '=' in a cell. The cell goes into Edit Mode. 
2. Use the Keyboard arrow keys to move in any direction. The Cell reference of the focused cell is automatically entered after the '=' into the cell which is in edit mode.
3. The user can press the Control+Arrow Key to add a reference to an entire row or column of data.

Add support for digital signature in the XLSX format.

Add sheet list that allows activating a sheet similar to Excel.

Vertical and horizontal scroll bar moves too fast once outside of the Viewport and one is dragging the selection.

 RadSpreadsheetSheetSelector add options for disabling the reordering and the editing of the sheets 

Implement auto complete for ListDataValidationRule like in Excel.

Provide a way so one can change the default cell editor with a custom one.

The sheet selector should hide sheets when their visibility is set to hidden or very hidden. The context menu of the sheet selector should contain Hide and Unhide options that allow to hide a sheet or unhide one of the hidden sheets.

Implement pasting of images similar to Excel.