Solved! Go to Solution.
Have you looked at the concepts section in the flex viewer help:
http://resources.arcgis.com/en/help/flex-viewer/concepts/index.html#/Pop_up_configuration_files/01m3...
This should provide the tag references you are after.
You would be better off in the future posting flex viewer questions to this forum:
http://forums.arcgis.com/forums/111-ArcGIS-Viewer-for-Flex
Regards
Anthony