static int getContext_n = 3;

static S getContext(S text, int lineNr) {
  new L<S> l;
  L<S> lines = toLines(text);
  int from = max(0, lineNr-1-getContext_n);
  int to = min(l(lines), lineNr+getContext_n);
  for (int i = from; i < to; i++)
    l.add((i == lineNr-1 ? "* " : ". ") + lines.get(i));
  ret fromLines(l);
}