This doesn’t seem to work in the RTE.
The rich text editor doesn’t support all features used in this post; switching you to the Markdown editor
I also noticed that when I pasted this into the Markdown editor after using the copy code button on the documentation topics here on Meta, the brackets were automatically escaped with backslashes, which I had to manually remove.
I copied
[calendar]
[/calendar]
and after pasting it in the Markdown editor I had:
\[calendar\]
\[/calendar\]