TikTok and its Chinese parent company ByteDance have filed a petition with a US court, seeking to block a law that forces them to sell the social media app to a non-Chinese buyer or face a ban. They argue the legislation is unconstitutional, setting the stage for a historic legal battle. But first, China's President Xi Jinping has arrived in Serbia on the second leg of his European tour. He expects to receive a much warmer welcome than he did in France.