Gets or sets a value indicating how a GroupFooterBand is positioned on a page relative to its group's rows.
A GroupFooterUnion enumeration value.
The GroupUnion property is intended to specify whether group rows can be printed on different pages (in this case both GroupHeaderBand.GroupUnion and GroupUnion are set to None), or the entire group will be printed on a single page (if the GroupHeaderBand.GroupUnion is set to GroupUnion.WholePage).
Also, if a group can be split across pages, but you don't want a Group Header to be printed on a page if there is no data row below it (in case a group starts at the page bottom and there is only enough room for a Group Header), you may set the GroupHeaderBand.GroupUnion to GroupUnion.WithFirstDetail. In this case, if a Group Header is alone on a page, it will be moved to the beginning of the next page.
It is the same for the GroupFooter. If you don't want it to be printed alone on a page, you may set its GroupUnion to GroupFooterUnion.WithLastDetail, and the last group row from the previous page will be moved to the next page to be printed together with a Group Footer.