sendgrid/docs — pull request #651 by SeanKendle (2014-11-06 16:07:47+00:00)
Title: Making the JSON example complete as though you were reading the raw head...

Making the JSON example complete as though you were reading the raw headers themselves in the email's source

Adding an explicit example, and also telling developers the headers will be STRIPPED FROM THE FINAL EMAIL and to not expect the headers to be visible in the email's source upon receipt.