MTGA “tier protection”

Can you lose a tier rank by losing games in ranked play? By which I mean, Silver → Bronze, Gold → Silver, and so on. I know you can lose tiers within one rank, as in Gold 1 → Gold 2, but I have read that you cannot lose the “metal” you have achieved, e.g. Gold 4 → Silver 1. However, that reporting doesn’t sound entirely certain about it:

• Once you ascend into a new rank, you’re safe for the rest of the season. No matter how many times you lose, you can’t fall from a rank (e.g., from Gold 4 to Silver 1).

• Although losses can push you down a tier within a rank (e.g., from Gold 3 to Gold 4), there is some protection when you move into a tier. Although to my knowledge the exact workings have never been officially announced, I discovered empirically that in best-of-one you cannot fall a tier within a rank within 3 games of reaching a new tier. So if you advance from Gold 4, step 5 to Gold 3, step 0 and then go loss-loss-loss or win-loss-loss, you’ll still be Gold 3, step 0 because of that 3-game protection. But if you lose again in your next game from that spot, you will drop to Gold 4, step 5. If you win immediately after that drop, then you’re back to Gold 3, step 0, with a 3-game protection.

The first point (which is my question) seems more certain, while the author expresses uncertainty about the second point (which I have experienced first-hand and can broadly corroborate), but as the author is not on Wizards of the Coast staff and doesn’t seem entirely sure about at least some of his information, I wanted to double-check.

Is it part of the official rules that you cannot lose a rank “metal” for lack of a better word? Where can that rule be found? Or, if it has not been explicitly documented/confirmed by Wizards of the Coast, where can I find significant fan testing of the idea, demonstrating it to be true?