Hello MyKey0815,
try this:
<Style TargetType="{x:Type xcdg:HierarchicalGroupByControl}">
Gregor Glinka
try this:
<Style TargetType="{x:Type xcdg:HierarchicalGroupByControl}">
<Setter Property="NoGroupContent"
Value="Hello World" />
</Style>
Gregor Glinka