What does Daniel 6:12 mean?

So they went straight to the king and brought up the law he had made. They asked, 'Didn't you sign a rule that says anyone who prays to any god or person besides you, Your Majesty, will be thrown into the lions' den?' The king answered, 'Yes, that's the law. It's official and can't be changed, just like all the laws of the Medes and Persians.' Daniel 6:12 - Modern Text Bible

(Daniel's accusers remind the king of his own law, making sure he can't back out of it. The law is set in stone, according to their customs.)