The containerClass hint for web-panels in JIRA server does not appear to work

At the bottom of this page, there is a hint that says you should be able to add a param tag with the name containerClass and that the value of that tag should be applied as a css class to the enclosing div, but when it does not seem to work on JIRA server v7.2.2#72004-sha1:9d51328

I copied the example directly as shown and the class did not appear on any div in the page. Is there some additional thing I need to do for this? Or is this documentation out of data?