Hover feature on a custom form

The 'extra details' hover uses the editor presentation for the work item type to determine which attributes to show. This can be 
configured in the process specification section: Configuration Data / Work Items / Editor Presentations. 
If there is an specific attribute that it is not working, please add a comment at the following Enhancement on jazz.net to raise this 
question: Enhancement 154620 - 
https://jazz.net/jazz/web/projects/Rational%20Team%20Concert#action=com.ibm.team.workitem.viewWorkItem&id=154620. 
 
There is a good documentation about the HOver features available at
https://jazz.net/wiki/bin/view/Main/WebRichHovers2010 (links) and 
https://jazz.net/wiki/bin/view/Main/ItemLevelInteractions2010 (actions items). 

Hi Sean, in the Editor Presentation, when you edit the presentation of an attribute the "Description" acts as a tool tip text and yes it should work for both web and eclipse client.
To add a little extra, if you want the tool tip text to be multiline then you may want to look at my answer on this post.