The ADempiere 370 Swing client allowed to embed a tab grid into another tab. So you could see an invoice and the invoice lines at the same time. I can't find a link to an exact picture of the old feature but I think it derived from this article: http://www.adempiere.com/Collapse_Grid_%26_Horizontal_Tab
We can find out why it doesn't work anymore and repair it or rethink the whole layout and do it a bit more like in zk. Or we can do both and make it even better.