I don’t understand the change to elf trance. Why do they suddenly no longer need to finish the 8 hours? Trance didn't change. The wording for long rests did. The new interpretation syncs Trance up with that wording.

— Jeremy Crawford (@JeremyECrawford) August 31, 2017

I looked at the PHB errata and didn’t understand what changed. Sounds like more arguments with elf players about how long they long rest for No need to argue. The DM decides how the rule works and can use the new ruling if it suits the campaign.

— Jeremy Crawford (@JeremyECrawford) August 31, 2017

@JeremyECrawford what specific duration is this referring to? Long rest = 4 hours total? Or trance 4 hours + 2 hours light activity? pic.twitter.com/Ihs8ITc4Ii

— Joshua lambert (@Jlambert384) September 1, 2017

The duration of the rest

— Jeremy Crawford (@JeremyECrawford) September 1, 2017