// tok must come from htmlTok
// returns content of all container tags found as CNC
// should be OK for both HTML and XML
static LL<S> stringContentsOfFirstContainerTag(L<S> tok, S tag) {
  ret join(contentsOfContainerTag(first(findContainerTag(tok, tag))));
}

static LL<S> stringContentsOfFirstContainerTag(S html, S tag) {
  ret stringContentsOfFirstContainerTag(htmlTok(html), tag);
}