svoid makeNotifyingStringBufferRotate(NotifyingStringBuffer buf, IF0<Int> getMaxChars) {
  buf.onChange(r {
    Int max = getMaxChars();
    if (max == null || buf.length() <= max) ret;
     
    try {
      int newLength = max/2;
      int ofs = buf.length()-newLength;
      S newString = buf.substring(ofs);
      buf.setLength(0);
      buf.append("[...] ").append(newString);
    } catch (Exception e) {
      buf.setLength(0);
    }
    buf.trimToSize();
  });
}