static S htag(S tag) {
  ret htag(tag, "");
}

static S htag(S tag, S contents, O... params) {
  new StringBuilder buf;
  buf.append("<" + tag);
  for (int i = 0; i < l(params); i += 2) {
    S name = (S) get(params, i);
    O val = get(params, i+1);
    if (nempty(name) && val != null) {
      S s = str(val);
      if (!empty(s))
        buf.append(" " + name + "=" + htmlQuote(s));
    }
  }
  S s = str(contents);
  if (empty(s))
    buf.append("/>");
  else
    buf.append(">" + s + "</" + tag + ">");
  ret str(buf);
}

// shortcut for converting an object to string
static S htag(S tag, O contents, O... params) {
  ret htag(tag, str(contents), params);
}