Selecting a column with two or more merged cells, selects not only the selected column but the rest of columns that the merged cells are from. The behavior when working with rows is analogical.

The fill selection stops working, after a filtering is applied and the currently selected cell is filtered out (it gets hidden). This prevents from displaying the fill selection cross displayed when you hover the bottom right corner of a selected cell. Any further changes in the selection doesn't re-enable the selection fill feature.

To work this around, you can set the IsEnabled property of the FillSelection on selection changed.

private RadWorksheetEditor activeWorksheetEditor;

public MainWindow()
{
  InitializeComponent();

  this.spreadsheet.ActiveSheetEditorChanged += (s, e) =>
  {
 if (activeWorksheetEditor != null)
 {
 activeWorksheetEditor.Selection.SelectionChanged -= Selection_SelectionChanged;
 }

 activeWorksheetEditor = this.spreadsheet.ActiveWorksheetEditor;
 activeWorksheetEditor.Selection.SelectionChanged += Selection_SelectionChanged;
  };
}

private void Selection_SelectionChanged(object? sender, EventArgs e)
{
  this.spreadsheet.ActiveWorksheetEditor.Selection.FillSelection.IsEnabled = true;
}

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.

Check how the performance can be improved in this scenario. The StyleGallery is taking much time to load, the GetUsedCellRange method is called multiple times.

The numeric box that allows you to select the "to" page in the PrintPreviewControl is clipped when the "Pages:" and "to" strings are translated to a language where these words are longer. For example, this reproduces with Dutch culture which uses the "Pagina's:" and "naar" texts.

To work this around, you can get the Grid panel that hosts the content and increase the Width of one of its ColumnDefinitions.

  private void PrintPreviewControl_Loaded(object sender, RoutedEventArgs e)
  {
      var printPreview = (PrintPreviewControl)sender;
      var rootGrid = printPreview.FindChildByType<Grid>();
      rootGrid.ColumnDefinitions[0].Width = new GridLength(355);
  }

Add an event that indicates when a hyperlink is clicked.

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.