// drop opening and closing tag, return new CNC
static L<S> contentsOfContainerTag(L<S> tok) {
  ret tok == null ? null : subList(tok, 2, l(tok)-2);
}

static L<S> contentsOfContainerTag(L<S> tok, S tagName) {
  ret contentsOfContainerTag(first(findContainerTag(tok, tagName)));
}