code: function() {
  
              var self = this;
              var $element = $(this.element);
  
              // save this id attribute.
              // it will be used as an unique id to identify this 
              // bilevel sunburst chart.
              self.attrId = $element.attr('id');
              //$element.html("I am sunburst! I am comming up now...");
              // get ready the scale colors.
              self.hue = d3.scale.category20c();
              self.luminance = d3.scale.sqrt()
                  .domain([0, 1e6])
                  .clamp(true)
                  .range([90, 20]);
  
              // format number.
              self.formatNumber = d3.format(",d");
              self.formatPercentage = d3.format(".2%");
  
              // get ready the d3.svg.arc object.
              self.arc = d3.svg.arc()
                  .startAngle(function(d) { return d.x; })
                  .endAngle(function(d) { return d.x + d.dx ; })
                  .padAngle(.01)
                  //.padRadius(self.options.diameter / (2 * 3))
                  // 6 = 2 * 3, we are using diameter instead of 
                  // radius, 
                  .padRadius(self.options.diameter / 6)
                  .innerRadius(function(d) { 
                      return self.options.diameter / 6 * d.depth; 
                  })
                  .outerRadius(function(d) { 
                      return self.options.diameter / 6 * (d.depth + 1) - 1; 
                  });
  
              // append the explanation div.
              self.appendExplanationDiv();
              // draw the sunburst chart.
              self.draw();
              // apply the stles for explanation.
              self.applyExplanationStyles();
          }
docs: initialize function