<text id="thingyouhoverover" x="50" y="35" font-size="14">Mouse over me!</text>
<text id="thepopup" x="250" y="100" font-size="30" fill="black" visibility="hidden">Change me
<set attributeName="visibility" from="hidden" to="visible" begin="thingyouhoverover.mouseover" end="thingyouhoverover.mouseout"/>