function d3_transition(groups, id, time) {

  d3_arraySubclass(groups, d3_transitionPrototype);

  var tweens = {},

      event = d3.dispatch("start", "end"),

      ease = d3_transitionEase;

  groups.id = id;

  groups.time = time;

  groups.tween = function(name, tween) {

    if (arguments.length < 2) return tweens[name];

    if (tween == null) delete tweens[name];

    else tweens[name] = tween;

    return groups;

  };

  groups.ease = function(value) {

    if (!arguments.length) return ease;

    ease = typeof value === "function" ? value : d3.ease.apply(d3, arguments);

    return groups;

  };

  groups.each = function(type, listener) {

    if (arguments.length < 2) return d3_transition_each.call(groups, type);

    event.on(type, listener);

    return groups;

  };

  d3.timer(function(elapsed) {

    groups.each(function(d, i, j) {

      var tweened = [],

          node = this,

          delay = groups[j][i].delay,

          duration = groups[j][i].duration,

          lock = node.__transition__ || (node.__transition__ = {active: 0, count: 0});

      ++lock.count;

      delay <= elapsed ? start(elapsed) : d3.timer(start, delay, time);

      function start(elapsed) {

        if (lock.active > id) return stop();

        lock.active = id;

        for (var tween in tweens) {

          if (tween = tweens[tween].call(node, d, i)) {

            tweened.push(tween);

          }

        }

        event.start.call(node, d, i);

        if (!tick(elapsed)) d3.timer(tick, 0, time);

        return 1;

      }

      function tick(elapsed) {

        if (lock.active !== id) return stop();

        var t = (elapsed - delay) / duration,

            e = ease(t),

            n = tweened.length;

        while (n > 0) {

          tweened[--n].call(node, e);

        }

        if (t >= 1) {

          stop();

          d3_transitionInheritId = id;

          event.end.call(node, d, i);

          d3_transitionInheritId = 0;

          return 1;

        }

      }

      function stop() {

        if (!--lock.count) delete node.__transition__;

        return 1;

      }

    });

    return 1;

  }, 0, time);

  return groups;

}

var d3_transitionRemove = {};

function d3_transitionNull(d, i, a) {

  return a != "" && d3_transitionRemove;

}

function d3_transitionTween(name, b) {

  var interpolate = d3_interpolateByName(name);

  function transitionFunction(d, i, a) {

    var v = b.call(this, d, i);

    return v == null

        ? a != "" && d3_transitionRemove

        : a != v && interpolate(a, v);

  }

  function transitionString(d, i, a) {

    return a != b && interpolate(a, b);

  }

  return typeof b === "function" ? transitionFunction

      : b == null ? d3_transitionNull

      : (b += "", transitionString);

}

var d3_transitionPrototype = [],

    d3_transitionId = 0,

    d3_transitionInheritId = 0,

    d3_transitionEase = d3.ease("cubic-in-out");

d3_transitionPrototype.call = d3_selectionPrototype.call;

d3.transition = function() {

  return d3_selectionRoot.transition();

};

d3.transition.prototype = d3_transitionPrototype;