What is meant by "We have not neglected anything in the Register" in the Qur’an?

The words of Allah Almighty: "We have not neglected in the Register a thing" (Quran 6:38) are interpreted in two ways: either "the Register" refers to the Preserved Tablet (Al-Lawh Al-Mahfuz), or it refers to the Quran. If it is the Quran, then the verse means that everything a Muslim needs in their religion is made clear therein, either explicitly, or generally, or by inference.