text: import "../format/collapse";
  import "../format/requote";
  import "selection";
  
  d3_selectionPrototype.classed = function(name, value) {
    if (arguments.length < 2) {
  
      // For classed(string), return true only if the first node has the specified
      // class or classes. Note that even if the browser supports DOMTokenList, it
      // probably doesn't support it on SVG elements (which can be animated).
      if (typeof name === "string") {
        var node = this.node(),
            n = (name = d3_selection_classes(name)).length,
            i = -1;
        if (value = node.classList) {
          while (++i < n) if (!value.contains(name[i])) return false;
        } else {
          value = node.getAttribute("class");
          while (++i < n) if (!d3_selection_classedRe(name[i]).test(value)) return false;
        }
        return true;
      }
  
      // For classed(object), the object specifies the names of classes to add or
      // remove. The values may be functions that are evaluated for each element.
      for (value in name) this.each(d3_selection_classed(value, name[value]));
      return this;
    }
  
    // Otherwise, both a name and a value are specified, and are handled as below.
    return this.each(d3_selection_classed(name, value));
  };
  
  function d3_selection_classedRe(name) {
    return new RegExp("(?:^|\\s+)" + d3.requote(name) + "(?:\\s+|$)", "g");
  }
  
  function d3_selection_classes(name) {
    return name.trim().split(/^|\s+/);
  }
  
  // Multiple class names are allowed (e.g., "foo bar").
  function d3_selection_classed(name, value) {
    name = d3_selection_classes(name).map(d3_selection_classedName);
    var n = name.length;
  
    function classedConstant() {
      var i = -1;
      while (++i < n) name[i](this, value);
    }
  
    // When the value is a function, the function is still evaluated only once per
    // element even if there are multiple class names.
    function classedFunction() {
      var i = -1, x = value.apply(this, arguments);
      while (++i < n) name[i](this, x);
    }
  
    return typeof value === "function"
        ? classedFunction
        : classedConstant;
  }
  
  function d3_selection_classedName(name) {
    var re = d3_selection_classedRe(name);
    return function(node, value) {
      if (c = node.classList) return value ? c.add(name) : c.remove(name);
      var c = node.getAttribute("class") || "";
      if (value) {
        re.lastIndex = 0;
        if (!re.test(c)) node.setAttribute("class", d3_collapse(c + " " + name));
      } else {
        node.setAttribute("class", d3_collapse(c.replace(re, " ")));
      }
    };
  }
  