static S structTokWordWrap(S s) {
  ret structTokWordWrap(120, s);
}

// TODO: complete trimming
static S structTokWordWrap(int cols, S s) {
  int col = 0;
  L<S> tok = structTok(s);
  for (int i = 0; i < l(tok); i++) {
    S t = tok.get(i);
    if (odd(i) && col >= cols && !containsNewLine(t))
      tok.set(i, t = rtrimSpaces(t) + "\n");
    int idx = t.lastIndexOf('\n');
    if (idx >= 0) col = l(t)-(idx+1);
    else col += l(t);
  }
  ret join(tok);
}