I’m guessing based on the username OP is the original author, caught a typo that could trip a novice up if they’re reading :

This becomes useful though if you send a request including a Except: 100-continue header. That header tells the server you expect a 100 response, and you're not going to send the full request body until you receive it.

I’m guessing that should be Expect?

Overall interesting article, thanks for writing it!