Adding a title attribute to svg:g element in D3.js
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I'm building an app with D3.js that displays a data in a tree-map. Ideally what I would like to is give the tree-map a tool-tip to display more info on each node of the tree-map. The tree-map is fed data from a .JSON file.

I am currently working with the jquery plug-in `Poshy Tip` where I can pass this info through the `title=` attribute. I know I need to somehow add the title attribute to the svg:g element in the tree-map but I can't figure out where I set each nodes title attr.   

Heres the beginning of my script where I make all my declarations etc...

    <div id="chart"></div>
    <script type="text/javascript">
    var tree = d3.layout.tree()
    .size([h, w - 160]);

    var diagonal = d3.svg.diagonal()
    .projection(function(d) { return [d.y, d.x]; });

    var vis = d3.select("#chart").append("svg:svg")
    .attr("width", w)
    .attr("height", h)
    .append("svg:g")
    .attr("transform", "translate(40,0)");

    d3.json("test.json", function(json) {
      json.x0 = 800;
      json.y0 = 0;
      update(root = json);
    });


Here is how I am using `poshytip()` in the head

    $(function(){
	$('node').poshytip({slide: false, followCursor: true, alignTo: 'cursor', 
    showTimeout: 0, hideTimeout: 0, alignX: 'center', alignY: 'inner-bottom',
    className: 'tip-twitter'});
	}


Pretty much I just want to be able to "mouseover" the individual items in the interactive tree-map and get a tooltip to pop-up.. but i havent had any luck. How can I set each item to have a specific Id.. do I do that in the .JSON file? Is there an easier way to do this? Am I going about this in the wrong manner? Any help would be great.