var myrules = {
  'form' : function(element) { // mejorable
    element.onsubmit = function() {
      for (var i = 0; i < element.getElementsByTagName('input').length; i++) {
        var el = element.getElementsByTagName('input')[i];
        if (el.value == el.rel)
          el.value = '';
      }
      for (var i = 0; i < element.getElementsByTagName('textarea').length; i++) {
        var el = element.getElementsByTagName('textarea')[i];
        if (el.value == el.rel)
          el.value = '';
      }
    }
  },
  '.js_reset' : function(element) {
    if (!element.rel)
      element.rel = element.value;
    element.onfocus = function() {
      if (element.value == element.rel)
        element.value = '';
    }
    element.onblur = function() {
      if (element.value == '')
        element.value = element.rel;
    }
  }
}

Behaviour.register(myrules);