Effective December 19, 2013, we removed the "Additional Content" option within the News/Resource Content List tool.
The additional content, and its predecessor options, have been troublesome and not compliant with current website standards. The overlay window doesn't work correctly on many mobile platforms, and is rapidly becoming incompatible with modern browsers and web languages.
Overlay windows are not always a positive user experience, and overlay windows on a mobile browser can be frustrating or worse, not work at all, for your users.
Current best practices indicate that content should be entered directly to a web page or even to a pdf. Either option is preferred over any type of overlay. Instead of creating an overlay window, we will be encouraging the use of a web page (inactive if applicable), or link to that PDF. In a mobile and tablet browser, the PDF or web page opens with no issues and the user has more control over the content then.
If you currently have a tool/item that is using that additional content overlay, that will stay for now. We just aren't sure how much longer those overlay windows will work on various browsers and platforms, so we will be encouraging everyone to redo that content to a different method/tool.