[pdftex] Hover effects in pdftex.

[John R. Culleton]

It is possible in hmtl, with a little help from Java or
Javascript, to create a "hover" effect. When the mouse moves
over a link something happens such as a box with text in it
appearing and temporarily overlaying what is underneath. It
seems to me I saw a pdf file that did the same, but I can't
recall where. 

Is there a mechanism in pdftex that (in combination with an online
viewer) allows this effect to be achieved? If so where is it
documented? 

All assistance appreciated.
-- 
John Culleton
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