in src/core/Node.hack [103:121]
final public function appendChild(mixed $child): this {
if ($this->__isRendered) {
throw new UseAfterRenderException(
Str\format("Can't %s after render", __FUNCTION__),
);
}
if ($child is Traversable<_>) {
foreach ($child as $c) {
$this->appendChild($c);
}
} else if ($child is frag) {
foreach ($child->getChildren() as $new_child) {
$this->children[] = $new_child;
}
} else if ($child !== null) {
$this->children[] = $child as \XHPChild;
}
return $this;
}