function check_comments(){
  var msg='';
  if(document.comment_form.name.value==""){
    msg+="Name\n";
  }
  if(document.comment_form.location.value==""){
    msg+="Location\n";
  }
  if(document.comment_form.comments.value==""){
    msg+="Comments\n";
  }
  if(document.comment_form.rcode.value==""){
    msg+="Verification code\n";
  }

  if(msg!=""){
    alert("You have not filled in:\n\n"+msg);
    return false;
  }

}