Thanks for the replies, and especially to you, Leon!
The reason I was asking was because of this thread:
http://forum.12oclockhigh.net/showthread.php?t=21085
An eye witness thought that the surviving Germans set fire to the landed Heinkel He 111. Since this was in April 1940 and predates the official order, it may have been just an unwritten rule to destroy the aircraft as much as possible if forced to land. Unless there is something older than "
Beschreibung und Bedienungsvorschrift für die Vernichtungsmittel von Landflugzeugen bei Notlandung auf Feindgebiet", that is.
Anyway, it only makes sense to destroy it as much as possible.