adding notes and nodes along a line graph like google analytics, adding pins to map locations, establishing a reference point with additional information. So: A little thing that indicates, and clicking gives you a little more data, which may well NOT be in the little icon, hence it's not just an Icon (which see) and is a different item. ALSO see the eReader project where the highlight can be selected and show more info (not a Tooltip, though, as that is limited, read only, etc.)

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