silverstripe/silverstripe-framework — pull request #2105 by Firesphere (2013-06-16 12:14:01+00:00)
Title: ENHANCEMENT Allow nested grouping

Make the children of a GroupedList a GroupedList too, to enable nested grouping in the template.
Known issue:
To get the groupname above the children, the index needs to be addressed with a double Up in the template.
```
<% loop Object.GroupedBy(Name) %>
<% loop Children.GroupedBy(LastName) %>
$Up.Up.Name
<% end_loop %>
<% end_loop %>
```