text: var margin = [20, 120, 20, 140],
      width = 4000 - margin[1] - margin[3],
      height = 900 - margin[0] - margin[2],
      i = 0,
      duration = 1250,
      root;
  
  var tree = d3.layout.tree()
      .size([height, width]);
  
  var diagonal = d3.svg.diagonal()
      .projection(function(d) { return [d.y, d.x]; });
  
  var vis = d3.select("#body").append("svg:svg")
      .attr("width", width + margin[1] + margin[3])
      .attr("height", height + margin[0] + margin[2])
    .append("svg:g")
      .attr("transform", "translate(" + margin[3] + "," + margin[0] + ")");
  
  d3.json("arf.json", function(json) {
    root = json;
    root.x0 = height / 2;
    root.y0 = 0;
  
    function collapse(d) {
      if (d.children) {
        d._children = d.children;
        d._children.forEach(collapse);
        d.children = null;
      }
    }
  
  /*  function toggleAll(d) {
      if (d.children) {
        d.children.forEach(toggleAll);
        toggle(d);
      }
    } */
    root.children.forEach(collapse);
    update(root);
  });
  
  function update(source) {
    // var duration = d3.event && d3.event.altKey ? 5000 : 500;
  
    // Compute the new tree layout.
    var nodes = tree.nodes(root).reverse();
  
    // Normalize for fixed-depth.
    nodes.forEach(function(d) { d.y = d.depth * 180; });
  
    // Update the nodes…
    var node = vis.selectAll("g.node")
        .data(nodes, function(d) { return d.id || (d.id = ++i); });
  
    // Enter any new nodes at the parent's previous position.
    var nodeEnter = node.enter().append("svg:g")
        .attr("class", "node")
        .attr("transform", function(d) { return "translate(" + source.y0 + "," + source.x0 + ")"; })
        .on("click", function(d) { toggle(d); update(d); });
  
    nodeEnter.append("svg:circle")
        .attr("r", 1e-6)
        .style("fill", function(d) { return d._children ? "lightsteelblue" : "#fff"; });
  
    nodeEnter.append('a')
        .attr("target", "_blank")
        .attr('xlink:href', function(d) { return d.url; })
        .append("svg:text")
        .attr("x", function(d) { return d.children || d._children ? -10 : 10; })
        .attr("dy", ".35em")
        .attr("text-anchor", function(d) { return d.children || d._children ? "end" : "start"; })
        .text(function(d) { return d.name; })
        .style("fill: rgb(0, 0, 0)", function(d) { return d.free ? 'black' : '#999'; })
        .style("fill-opacity", 1e-6);
  
    nodeEnter.append("svg:title")
      .text(function(d) {
        return d.description;
      });
  
    // Transition nodes to their new position.
    var nodeUpdate = node.transition()
        .duration(duration)
        .attr("transform", function(d) { return "translate(" + d.y + "," + d.x + ")"; });
  
    nodeUpdate.select("circle")
        .attr("r", 6)
        .style("fill", function(d) { return d._children ? "lightsteelblue" : "#fff"; });
  
    nodeUpdate.select("text")
        .style("fill-opacity", 1);
  
    // Transition exiting nodes to the parent's new position.
    var nodeExit = node.exit().transition()
        .duration(duration)
        .attr("transform", function(d) { return "translate(" + source.y + "," + source.x + ")"; })
        .remove();
  
    nodeExit.select("circle")
        .attr("r", 1e-6);
  
    nodeExit.select("text")
        .style("fill-opacity", 1e-6);
  
    // Update the links…
    var link = vis.selectAll("path.link")
        .data(tree.links(nodes), function(d) { return d.target.id; });
  
    // Enter any new links at the parent's previous position.
    link.enter().insert("svg:path", "g")
        .attr("class", "link")
        .attr("d", function(d) {
          var o = {x: source.x0, y: source.y0};
          return diagonal({source: o, target: o});
        })
      .transition()
        .duration(duration)
        .attr("d", diagonal);
  
    // Transition links to their new position.
    link.transition()
        .duration(duration)
        .attr("d", diagonal);
  
    // Transition exiting nodes to the parent's new position.
    link.exit().transition()
        .duration(duration)
        .attr("d", function(d) {
          var o = {x: source.x, y: source.y};
          return diagonal({source: o, target: o});
        })
        .remove();
  
    // Stash the old positions for transition.
    nodes.forEach(function(d) {
      d.x0 = d.x;
      d.y0 = d.y;
    });
  }
  
  // Toggle children.
  function toggle(d) {
    if (d.children) {
      d._children = d.children;
      d.children = null;
    } else {
      d.children = d._children;
      d._children = null;
    }
  }