d3_transitionPrototype.attr = function(name, value) {
  return this.attrTween(name, d3_transitionTween(name, value));
};

d3_transitionPrototype.attrTween = function(nameNS, tween) {
  var name = d3.ns.qualify(nameNS);

  function attrTween(d, i) {
    var f = tween.call(this, d, i, this.getAttribute(name));
    return f === d3_transitionRemove
        ? (this.removeAttribute(name), null)
        : f && function(t) { this.setAttribute(name, f(t)); };
  }

  function attrTweenNS(d, i) {
    var f = tween.call(this, d, i, this.getAttributeNS(name.space, name.local));
    return f === d3_transitionRemove
        ? (this.removeAttributeNS(name.space, name.local), null)
        : f && function(t) { this.setAttributeNS(name.space, name.local, f(t)); };
  }

  return this.tween("attr." + nameNS, name.local ? attrTweenNS : attrTween);
};