[VB6, Vista+] Undocumented ListView feature: Subsetted Groups (simple, no TLB)

[fafalone]

Wow that's an insanely complex control.. but no it doesn't support subsetting groups, because it doesn't use group view in any of its modes (the LVM_ messages and LVGROUP structure aren't even declared). Not to mention it looks like absolutely everything is owner-drawn. If you wanted to do it, it would have to be completely from scratch. Even if you added group view support, a challenge on its own, I don't know that the owner-draw code wouldn't override subsetting.
If you really think its worthwhile, read up on ListView Group API, look at existing group view code. Minus the owner-draw issue, the listview is API-created and the ucVHGrid.hWnd is the ListView hWnd that you would send the messages to (LVM_INSERTGROUP, LVM_ENABLEGROUPVIEW, LVM_SETGROUPSUBSETCOUNT, etc).
-Enable group view
-add groups
-when items are inserted their groupid must be set
-set subset count

Edit: Sorry, the situation is far worse than I thought. It doesn't even use items. The "items" aren't even listitems, the exist entirely as manually-drawn custom objects. Regular ListView items are LVITEM structures added through LVM_INSERTITEM; neither of those exist in this control. So the only practical way to add subsetting would be manually drawing the text and link after adding a given number of items, then adding the rest on click. But there's absolutely nothing that would handle that even partially for you, it would have to be drawn from scratch with APIs like DrawText.