Event.observe(window, 'load', function() {
  $$('div#main-text a[href!=""]').each(function(link){
    var siteregex = /^((http|https):\/\/)([a-z]*\.)?(funstorm.cz)/i;
    if((link.readAttribute('href').startsWith('http://') || link.readAttribute('href').startsWith('https://')) && !link.readAttribute('href').match(siteregex)){
      link.writeAttribute('target', '_blank');
      link.writeAttribute('rel', 'external');
    }
  });
});