Element.addMethods('INPUT', {
  autoCompletion: function(input, afterUpdateElement){
    if(!input.ac){
      input.ac = new Ajax.Autocompleter(input, input.id+'_auto_complete', input.getAttribute('src'), {
          method: 'get',
          select: 'value',
          callback: function(element, value){
            document.enabled = true;
            return element.serialize();
          },
          afterUpdateElement: function(input, element){
            input.indicate();
            document.ajaxRequest(input, input.getAttribute('usemap'), 'put', null, input.serialize())
            if(input.hasClassName('clear')) input.value = '';
            if(afterUpdateElement) afterUpdateElement(input, element);
          }
      });
    };
  }
});

Element.addMethods({
  observeAutoCompletion: function(element){
    if( !(element = $(element))) return;
    element.select('input.ac').each(function(input){
      // adding autocompletion to that input (needs to observe keypress directly)
      input.autoCompletion();
    });
    // delegate onClick & onMouseMove to that element for all input.autocomplete inside
    if(!element.autoCompletion){
      element.observe('click', autoCompletionClick) // SelectButton
      element.observe('mousemove', autoCompletionMouseMove) // IE6 fix (ScrollBug)
      element.autoCompletion = true;
    };
  },
  unobserveAutoCompletion: function(element){
    if(element.autoCompletion){
      // remove observed Events (autoCompletionClick/ autoCompletionMouseMove/ KEYUP)
      element.stopObserving('click', autoCompletionClick)
      element.stopObserving('mousemove', autoCompletionMouseMove)
      element.select('input.ac').each(function(input){
        input.stopObserving('keyup');
        input.ac = null;
      });
      element.autoCompletion = false;
    };
  }
})