Just saw this today on the Flyertalk home page

"In the published ruling, the ECJ concluded that arrival time should be noted when passengers are able to leave the aircraft, instead of when the airplane physically arrives. BBC News reported the ruling stated that “the concept of ‘arrival time’, which is used to determine the length of the delay to which passengers on a flight have been subject, refers to the time at which at least one of the doors of the aircraft is opened.”"

How does one document when the plane door opens?