Series.Bubble - Using the Quicktips Element
    By default, a "quicktip" is displayed when the mouse hovers over a
 bubble: 
    
    The automatically-generated quicktip displays information from the X- and
 Y-axes and the bubble size, as shown above, left. However, you may want to
 display other information or format it differently, perhaps as shown above,
 right, which can be done by adding a 
Quicktip child element beneath
 Series.Bubble and setting its attributes and child elements. Use @Chart
 tokens to include chart data in the quicktip. Intrinsic functions are
 supported in the Quicktip attributes.