// if
block exists: put tag before
// if not: append to whole HTML
// TODO: use something better than findContainerTag
sS hAddToBody(S html, S contents) {
if (emptyAfterTrim(contents)) ret html;
L tok = htmlTok(html);
LS body = first(findContainerTag(tok, "body"));
if (body == null) ret joinWithEmptyLines(html, contents);
int i = l(body)-3;
body.set(i, joinWithEmptyLines(body.get(i), contents));
ret join(tok);
}