(function() {
  var nextKey = 0;

  function local() {
    return new Local;
  }

  function Local() {
    this._id = "@" + (++nextKey).toString(36);
  }

  Local.prototype = local.prototype = {
    constructor: Local,
    get: function(node) {
      var id = this._id;
      while (!(id in node)) if (!(node = node.parentNode)) return;
      return node[id];
    },
    set: function(node, value) {
      return node[this._id] = value;
    },
    remove: function(node) {
      return this._id in node && delete node[this._id];
    },
    toString: function() {
      return this._id;
    }
  };

  d3.local = local;
})();