GroupLevelDescriptions provide complementary information to the GroupDescriptions that are used to group that data items. That said, if you want to add group descriptions at runtime, you would need to add them to either the Items.GroupDescriptions collection (see ItemsControl), or to the DataGridCollectionView[Source] to which the grid is bound.

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Technical Writer - Xceed Software

Of all the things I've lost, I miss my mind the most. - Mark Twain