LHR to TXL, 19/01/2018, T5 Gate 12
Thanks to "severe delays" on the Piccadilly Line (i.e. a 35-minute gap between trains to T5), boarding was already well underway as I got to the gate but it appears to have been done by the book.
Three separate lanes, clearly signed as "Group 1", "Groups 2/3" and "Groups 4/5". The first two lanes were empty and there was a queue at the third. I walked up the empty lane 1 and was called forward immediately. As I went down the escalator the gate agent announced "If we could now have Group 4... Group 4 only, please come forward".
Very pleasantly surprised.