You can
1) define your text box with visibility="hidden" as
<g id="tooltip" transform="translate(0 0)">
<rect ................
<text id="tooltip_data ...............
</g>

2) For your objects, define event ( for your bars by example)
<rect onmouseover="show_tooltip('some text',40,200)" onmouseout="hide_tooltip()" .... />

3) Define functions
function show_tooltip(data,x_pos,y_pos)
{
svgdoc.getElementById("tooltip").setAttribute("tra nsform","translate(" + x_pos.toString() + " " + y_pos.toString() + ")")
svgdoc.getElementById("tooltip_data").firstChild.d ata = data
svgdoc.getElementById("tooltip").setAttribute("vis ibility","visible")
}

function hide_tooltip()
{
svgdoc.getElementById("tooltip").setAttribute("vis ibility","hidden")
}

Michel