  function chart(selection) {

    // Merging the various user params
    vars.user_vars = vistk.utils.merge(vars.user_vars, vars._user_vars);

    // Merging with current charts parameters set by the user in the HTML file
    vars = vistk.utils.merge(vars, vars.user_vars);

    // Create the top level element conaining the visualization
    if(!vars.svg) {
       if(vars.type !== "table") {
       
        vars.svg = d3.select(vars.container).append("svg")
          .attr("width", vars.width)
          .attr("height", vars.height)
          .style('overflow', 'visible')
          .style('z-index', 0)
          .append("g")
            .attr("transform", "translate(" + vars.margin.left + "," + vars.margin.top + ")");

      } else {
        // HTML Container for table
        vars.svg = d3.select(vars.container).append("div")
            .style({height: vars.height+"px", width: vars.width+"px", overflow: "scroll"});

      }
   }

  function chart(selection) {

    // Merging the various user params
    vars.user_vars = vistk.utils.merge(vars.user_vars, vars._user_vars);

    // Merging with current charts parameters set by the user in the HTML file
    vars = vistk.utils.merge(vars, vars.user_vars);

    // Create the top level element conaining the visualization
    if(!vars.svg) {
       if(vars.type !== "table") {
       
        vars.svg = d3.select(vars.container).append("svg")
          .attr("width", vars.width)
          .attr("height", vars.height)
          .append("g")
            .attr("transform", "translate(" + vars.margin.left + "," + vars.margin.top + ")");

      } else {
        // HTML Container for table
        vars.svg = d3.select(vars.container).append("div")
            .style({height: vars.height+"px", width: vars.width+"px", overflow: "scroll"});

      }
   }

--- 
+++ 
@@ -13,6 +13,8 @@
         vars.svg = d3.select(vars.container).append("svg")
           .attr("width", vars.width)
           .attr("height", vars.height)
+          .style('overflow', 'visible')
+          .style('z-index', 0)
           .append("g")
             .attr("transform", "translate(" + vars.margin.left + "," + vars.margin.top + ")");
 
Allow elements within SVG to overflow
