League\CommonMark\Block\Element\AbstractBlock::setParent PHP Method

    protected function setParent(Node $node = null)
    {
        if ($node && !$node instanceof self) {
            throw new \InvalidArgumentException('Parent of block must also be block (can not be inline)');
        }
        parent::setParent($node);
    }

 public function replaceChild(ContextInterface $context, AbstractBlock $original, AbstractBlock $replacement)
 {
     if (($index = $this->children->indexOf($original)) !== false) {
         $this->children->remove($index);
         $replacement->setParent($this);
         $this->children->set($index, $replacement);
     } else {
         $this->addChild($replacement);
     }
     if ($context->getTip() === $original) {
         $context->setTip($replacement);
     }
 }