Describes the cause and action for error messages.
Error Message(English)：
outline symbols missing
Hiding Outline Symbols (Microsoft Excel) - Excel Ribbon Tips - Tips.Net
https://excelribbon.tips.net/T009269_Hiding_Outline_Symbols.html
Hiding Outline Symbols (Microsoft Excel) - Excel Tips - Tips.Net
https://excel.tips.net/T003020_Hiding_Outline_Symbols.html
Hiding Group & Outline Symbols in Microsoft Excel 2010 - Excel Tip
https://www.exceltip.com/excel-grouping-and-outlining/hiding-group-outline-symbols-in-excel-2007.htm・・・
excel How to make the "+"symbol at the left side of the outline ...
https://stackoverflow.com/questions/5510001/excel-how-to-make-the-symbol-at-the-left-side-of-the-out・・・
microsoft excel - Row and Column grouping buttons have disappeared ...
https://superuser.com/questions/1065766/row-and-column-grouping-buttons-have-disappeared-on-certain-・・・
subtotal outline not working | PC Review
https://www.pcreview.co.uk/threads/subtotal-outline-not-working.3967087/
Excel: Group rows automatically or manually, collapse and expand rows
https://www.ablebits.com/office-addins-blog/2017/12/28/excel-group-rows/
How To Change Excel's Group Outline Direction Settings ? The ...
https://www.thespreadsheetguru.com/blog/change-excels-group-outline-direction-settings
Outline Excel Data in Microsoft Excel - Instructions - TeachUcomp, Inc.
https://www.teachucomp.com/outline-excel-data-in-microsoft-excel/