So, what's that above the e in Noël?
A correspondent clarifies:
"That's not an umlaut, which is used in German, but a dieresis, which is
used in English. The dieresis is used to indicate that two vowels are
separate, not a diphthong. I can remember when "coöperation" was common,
for example. Noël was used a lot, too. Now you don't see either so much."