2019-01-27 UTC
# 
sknebel it's standard, but I'd guess mostly used for consumers that explicitly try to download a full feed (e.g. site archiving tools etc), with many things that only are interested in recent changes assuming they'll crawl often enough and don't bother with it (but that's a guess, I haven't looked at what various things do in detail. the necessary info is in parser output, which is what I mostly work on)