Three pages on how drivechains actually work underneath — the eight messages, the escrow that governs sidechains and withdrawals, and the auction that moves a sidechain forward one block at a time.
One distinction organises the whole protocol, and most confusing failures come from missing it. Every drivechain message is either an output in a block's coinbase or an output in an ordinary transaction — and that decides who can produce it at all.
Produced solely by the miner who found the block, in practice one whose template comes from a BIP300/301 enforcer. Cannot be broadcast, cannot be forged.
Relayed through the mempool by anyone, mined by any miner, paying ordinary fees. Reaching the network and being accepted are different things.