d3_selectionPrototype.classed = function(name, value) {

  var names = name.split(d3_selection_classedWhitespace),

      n = names.length,

      i = -1;

  if (arguments.length > 1) {

    while (++i < n) d3_selection_classed.call(this, names[i], value);

    return this;

  } else {

    while (++i < n) if (!d3_selection_classed.call(this, names[i])) return false;

    return true;

  }

};

var d3_selection_classedWhitespace = /\s+/g;

function d3_selection_classed(name, value) {

  var re = new RegExp("(^|\\s+)" + d3.requote(name) + "(\\s+|$)", "g");

  // If no value is specified, return the first value.

  if (arguments.length < 2) {

    var node = this.node();

    if (c = node.classList) return c.contains(name);

    var c = node.className;

    re.lastIndex = 0;

    return re.test(c.baseVal != null ? c.baseVal : c);

  }

  function classedAdd() {

    if (c = this.classList) return c.add(name);

    var c = this.className,

        cb = c.baseVal != null,

        cv = cb ? c.baseVal : c;

    re.lastIndex = 0;

    if (!re.test(cv)) {

      cv = d3_collapse(cv + " " + name);

      if (cb) c.baseVal = cv;

      else this.className = cv;

    }

  }

  function classedRemove() {

    if (c = this.classList) return c.remove(name);

    var c = this.className,

        cb = c.baseVal != null,

        cv = cb ? c.baseVal : c;

    cv = d3_collapse(cv.replace(re, " "));

    if (cb) c.baseVal = cv;

    else this.className = cv;

  }

  function classedFunction() {

    (value.apply(this, arguments)

        ? classedAdd

        : classedRemove).call(this);

  }

  return this.each(typeof value === "function"

      ? classedFunction : value

      ? classedAdd

      : classedRemove);

}