var dwAvailabilityChecker = new Class({  
          
        //implements  
        Implements: [Options],  
      
        //options  
        options: {  
            trigger: 'keyup',  
            offset: { x:0, y:0 },  
           element: '',  
           minLength: 5,  
           availableClass: 'available',  
           takenClass: 'taken',  
           availableImage: '',  
           takenImage: '',  
           url: 'includes/ajax-username-check.php'  
       },  
         
       //initialization  
       initialize: function(options) {  
           //set options  
           this.setOptions(options);  
             
           //validate it  
           this.validate();  
       },  
         
       //a method that does whatever you want  
       validate: function() {  
           this.options.element.addEvent(this.options.trigger,function() {  
               if(this.options.element.value.length >= this.options.minLength) {  
                   var othis = this;  
                   var request = new Request({  
                       url: othis.options.url,  
                       method: 'get',  
                       data: {  
                           username: othis.options.element.value,  
                           ajax: 1  
                       },  
                       onRequest: function() {  
                           //remove existing classes  
                           othis.options.element.removeClass(othis.options.availableClass).removeClass(othis.options.takenClass);  
                       },  
                       onComplete: function(response) {  
                           //add class  
                           othis.options.element.addClass(response == 1 ? othis.options.availableClass : othis.options.takenClass);  
                           othis.injectImage(response == 1 ? othis.options.availableImage : othis.options.takenImage);  
                       }  
                   }).send();  
               }  
           }.bind(this));  
       },  
         
       //adds the image  
       injectImage: function(image) {  
             
           //figure out its position  
           var pos = this.options.element.getCoordinates();  
             
           var img = new Element('img',{  
               src: image,  
               styles: {  
                   'z-index': 100000,  
                   'position': 'absolute',  
                   'top': pos.top + this.options.offset.y,  
                   'left': pos.left + pos.width + this.options.offset.x  
               }  
           }).inject(document.body);  
             
             
       }  
         
   });