HML Checker

Add "Save Project File" to the file menu and the Ctrl+S shortcut.

Then implement code to write to the file, for CSV/TXT obviously save all as text with either comma or tab (\t) as the separating character, but for XLSX try to save the column cell type associated with the column and possibly any formatting that was originally associated with the worksheet if it was opened.

Note: If the worksheet was never saved before act as the "Save As" dialog (and for new unsaved Excel worksheets, bolden and freeze the top row on the saved worksheet).