function check_form() 
{
  validity = true; // assume valid 
  var error_txt ='';
  if (!check_empty(document.register_0.name.value))
  { 
      validity = false; 
      document.getElementById('name').className='alert'; error_txt ='Ihr Name fehlt<br>'; } else {document.getElementById('name').className='required';
  }
  if (!check_empty(document.register_0.vorname.value))
  { 
      validity = false; 
      document.getElementById('vorname').className='alert'; error_txt = error_txt +'Ihr Vorname fehlt<br>'; } else {document.getElementById('vorname').className='required';
  }
  if (!check_empty(document.register_0.street.value))
  { 
      validity = false; 
      document.getElementById('street').className='alert'; error_txt = error_txt +'Ihre Strasse fehlt<br>'; } else {document.getElementById('street').className='required';
  }
  if (!check_empty(document.register_0.city.value))
  { 
      validity = false; 
      document.getElementById('city').className='alert'; error_txt = error_txt +'Ihre Stadt fehlt<br>'; } else {document.getElementById('city').className='required';
  }
  
  if (!check_empty(document.register_0.email.value))
  { 
      validity = false; 
      document.getElementById('email').className='alert'; error_txt = error_txt +'Ihre Email-Adresse fehlt<br>'; } else {document.getElementById('email').className='required';
  }
  if (!check_empty(document.register_0.betreff.value))
  { 
      validity = false; 
      document.getElementById('betreff').className='alert'; error_txt = error_txt +'Ein Betreff fehlt<br>'; } else {document.getElementById('betreff').className='required';
  }
  /*
  if(error_txt.length > 0){
    document.getElementById('error_txt').innerHTML = '<font color="#ff0000" class="size8">'+ error_txt+'</font>';
    document.getElementById('error_tr').style.display='';
  } else {
    document.getElementById('error_tr').style.display='none';
  }
  */
  return validity;
}

function check_empty(text) {
  return (text.length > 0); // gibt false zurück wenn leehr
}

function check_email(address) {
  if ((address == "")
    || (address.indexOf ('@') == -1)
    || (address.indexOf ('.') == -1))
      return false;
  return true;
}