static S dropContainerTags(S s) {
  ret join(dropContainerTags(htmltok(s)));
}

static L<S> dropContainerTags(L<S> tok) {
  for (L<S> l : findContainerTags(tok))
    for (int i = 1; i < l(l)-1; i++)
      l.set(i, "");
  ret tok;
}