Describes the cause and action for error messages.
Error Message(English)：
group cannot create outline
How to get excel to auto-outline hierarchy into groups? - Super User
https://superuser.com/questions/748213/how-to-get-excel-to-auto-outline-hierarchy-into-groups
Bug with grouping in Excel 2016?
https://superuser.com/questions/1097660/bug-with-grouping-in-excel-2016
Excel 2010/13 and column grouping : how to ...
https://superuser.com/questions/587178/excel-2010-13-and-column-grouping-how-to-have-the-toggle-butt・・・
How to Group and Outline Excel Data: 14 Steps (with Pictures)
https://www.wikihow.com/Group-and-Outline-Excel-Data
How to Create Outline in a Worksheet in Excel 2016 - YouTube
https://www.youtube.com/watch?v=yGV4L227vJc
https://www.youtube.com/watch?v=yGV4L227vJc
How to Group Rows and Cells in Excel - and Outline them too
https://spreadsheeto.com/grouping-outlining/
Excel: Group rows automatically or manually, collapse and expand rows
https://www.ablebits.com/office-addins-blog/2017/12/28/excel-group-rows/
Microsoft Excel 2007: Outlining Worksheets - Small Business Computing
https://www.smallbusinesscomputing.com/buyersguide/article.php/3801786/Microsoft-Excel-2007-Outlinin・・・