Michelis,
I am not sure if this is what you are looking for, but please see the attached JPG.
This page is from a NetTalk app that shows the number of aircraft that land on each runway during specific time intervals. To view the callsigns of the aircraft that comprise that total, all the controller has to do is hover over the cell in the table. I believe this is the same functionality as the tooltip.
To create a linefeed, just insert 
 into the text. This is interpreted as a carriage return.
The problem I had was aligning the columns with the proportional-spaced font. I had to resort to weighting the text if it contained a "W" or "M" and insert a tab ( 	 ) or two to align the columns on the fixed tab stops. It mostly works, but there must be something a bit more elegant.
Cheers!
Rob
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