A protocol is a contract for interpretations of messages. "Backticks should be formatted as code in clients when they receive them in text messages" is part of the 'protocol' of Slack, even if it's implicit.
(More specifically, you can think of each message body as having a content-type, probably something like "text/x-vnd.com.slack-slackrichtext".)
(More specifically, you can think of each message body as having a content-type, probably something like "text/x-vnd.com.slack-slackrichtext".)