// returns: (CtxCase, closing line number)

// or null

static Pair<CtxCase, Int> ctxCase(L<S> lines, int i) {

  new Matches m;

  new CtxCase c;

  while (i <= l(lines) && emptyAfterTrim(get(lines, i))) ++i;

  S l = get(lines, i);

  if (startsWith(trim(get(lines, i+1)), ")")) {

    lines.set(i, l += get(lines, i+1));

    lines.remove(i+1);

  }

  if (jmatch("DEFAULT ACTION", l) || jmatch("ACTION", l)) {}

  else if (flexMatch("CASE (*) ACTION", l, m, false))

    c.condition = m.get(0);

  else null;

  Pair<SS, Int> p = ctxParseProperties(lines, i+1);

  c.properties = p.a;

  int opening = p.b;

  int closing = indexOfClosingCurlyBracket(lines, p.b);

  c.action = tok_unCurlyBracket(lines(subList(lines, p.b, closing+1)));

  ret pair(c, closing);

}