JavaScript: Inheritance John Resig

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//Simple Javascript Inheritance - John Resig
//example code
	var Person = Class.extend({
  init: function(isDancing){
    this.dancing = isDancing;
    },
    dance: function(){
      return this.dancing;
    }
  });
   
  var Ninja = Person.extend({
    init: function(){
      this._super( false );
    },
    dance: function(){
      // Call the inherited version of dance()
      return this._super();
    },
    swingSword: function(){
      return true;
    }
  });
   
  var p = new Person(true);
  p.dance(); // => true
   
  var n = new Ninja();
  n.dance(); // => false
  n.swingSword(); // => true
   
  // Should all be true
  p instanceof Person && p instanceof Class &&
  n instanceof Ninja && n instanceof Person && n instanceof Class  

//IMmplementation
/* Simple JavaScript Inheritance
 * By John Resig http://ejohn.org/
 * MIT Licensed.
 */
// Inspired by base2 and Prototype
(function(){
  var initializing = false, fnTest = /xyz/.test(function(){xyz;}) ? /\b_super\b/ : /.*/;
 
  // The base Class implementation (does nothing)
  this.Class = function(){};
 
  // Create a new Class that inherits from this class
  Class.extend = function(prop) {
    var _super = this.prototype;
   
    // Instantiate a base class (but only create the instance,
    // don't run the init constructor)
    initializing = true;
    var prototype = new this();
    initializing = false;
   
    // Copy the properties over onto the new prototype
    for (var name in prop) {
      // Check if we're overwriting an existing function
      prototype[name] = typeof prop[name] == "function" &&
        typeof _super[name] == "function" && fnTest.test(prop[name]) ?
        (function(name, fn){
          return function() {
            var tmp = this._super;
           
            // Add a new ._super() method that is the same method
            // but on the super-class
            this._super = _super[name];
           
            // The method only need to be bound temporarily, so we
            // remove it when we're done executing
            var ret = fn.apply(this, arguments);        
            this._super = tmp;
           
            return ret;
          };
        })(name, prop[name]) :
        prop[name];
    }
   
    // The dummy class constructor
    function Class() {
      // All construction is actually done in the init method
      if ( !initializing && this.init )
        this.init.apply(this, arguments);
    }
   
    // Populate our constructed prototype object
    Class.prototype = prototype;
   
    // Enforce the constructor to be what we expect
    Class.prototype.constructor = Class;
 
    // And make this class extendable
    Class.extend = arguments.callee;
   
    return Class;
  };
})();