Use this tag when the structure is like that one Repeater (Child) is placed inside another Repeater (Parent). Both Repeaters will bind from different Data Sources.
If you use Repeater in nested structure then you have to bind both Repeaters (Parent and Child) from different Data Sources (can be DataTable, List, Database etc).
The nested structure could be:
(-) Repeater -> Parent
(-) Controls
(+) Repeater -> Child
Note: Child Repeater will be bind in RowDataBound
event of Parent Repeater with C#.