Describes the cause and action for error messages.
Error Message(English)：
does not group columns
Grouping elements while exporting dataGridView to PDF using ...
https://stackoverflow.com/questions/31514070/grouping-elements-while-exporting-datagridview-to-pdf-u・・・
Graphical Column Schedule Tutorial | Tab (Gui) | Computer File - Scribd
https://es.scribd.com/document/232615329/Graphical-Column-Schedule-Tutorial
How to group columns in a pivot? - StackAnswers
https://stackanswers.net/questions/how-to-group-columns-in-a-pivot
Full text of "html_tutorial" - Internet Archive
https://archive.org/stream/html_tutorial_201801/html_tutorial_djvu.txt
Oreilly -html_and_xhtml_pocket_reference_ ... - SlideShare
https://www.slideshare.net/gajapandiyan/oreilly-htmlandxhtmlpocketreference28december20092928attica2・・・