Hi,

I found the icon code myself, but as for now, I have no idea where to look for if I would like to change to mouse over the subject

That's the point. Currently, the posting subject is not used by the JS. Thus, the bubble icon is an easy to use point of entry to implement this issue. We will add this issue within the version 2.4.x. The option is per default disabled and can be activate by setting ajax_preview=2.

One thing more... do you find it reasonable to show the bubble icon only when a post has a non-empty body text? This condition is already checked somewhere in the code, to determine if the "no_text.png" icon should be shown.

Good point, I add a feature request for version 2.4.x.

/Micha