@Override
  public PrintStream append(CharSequence csq, int start, int end) {
    CharSequence seq = csq == null ? "null" : csq;
    printed(seq.subSequence(start, end).toString());
    return this;
  }
Delegates all PrintStream invocations to {@link #printed(String)}.
Aims to keep the original invocation granularity.
spock-core/src/main/java/org/spockframework/util/StringMessagePrintStream.java