The value of this property is the name of a containing group (other than the current group) or data set over which to apply the hiding. Each time a new instance of that group is encountered, the first visible instance of this report item will not be hidden. Rows on a previous page are ignored for the purposes of hiding duplicates.
If the current textbox is in a Tablix cell, only the text will be omitted. The text box will remain to provide background and border for the cell. Outside of a tablix cell, the background and borders are omitted as well. Ignored unless the text box contains only one TextRun.