pocketmine\level\Level::isFullBlock PHP Method

    public function isFullBlock(Vector3 $pos) : bool
    {
        if ($pos instanceof Block) {
            if ($pos->isSolid()) {
                return true;
            }
            $bb = $pos->getBoundingBox();
        } else {
            $bb = $this->getBlock($pos)->getBoundingBox();
        }
        return $bb !== null and $bb->getAverageEdgeLength() >= 1;
    }