Though this functionality is provided by the 'expand' user macro as James has pointed out, I would like to attach this comment to my vote to urge Atlassian to consider making the 'expand' user macro functionality part of one of Atlassian's plugins. That is, I would like to request that 'expand' be officially supported.
My company has a space that makes extensive use of the 'expand' macro, and the 'expanded' content often involves including other pages that themselves have 'expand' macros within their content, coupled with photos in thumbnail and nested table content. That is to say that our use of 'expand' is both extensive and complex. Each time we upgrade to a new version of Confluence, our 'expand' formatting breaks due to some change in the underlying Confluence code and this affects over 99% of the content in one of our spaces – the one space that was the initial justification for us to buy Confluence in the first place. This "breaking upon upgrading" which comes from 'expand' not being officially supported or tested with each release makes it very difficult for me to justify upgrades, and is extremely time-consuming as I attempt to pursue workarounds or fixes in the user community.
I think there is a sufficiently large user community that uses this macro (as evidenced by the comments on http://confluence.atlassian.com/display/CONFEXT/Expand+Text+User+Macro – and I've also heard that 'expand' is used quite extensively within Atlassian, too. Please consider providing the 'expand' functionality as part of a plugin and officially supporting this functionality in future releases.
Thank you!
Julie
Just a little comment. With the latest version and Firefox there is a ugly border around the div that denotes the expand block. This border appears after expand is first clicked and remains until the page refreshes completely. I just noticed that the old expand macro version didn't have this problem (but did have others).