How is "Expand"-macro defined in Atlassian Document Format?

I am currently working on an application where I want to post comments with the JIRA API to JIRA. I am working with Atlassian Document Format and one of my comments need to contain the “Expand”-macro. However, when I am looking at the documentation I can’t find anything about the “Expand”-macro.

Does anyone know how to do it or is it not possible?