Within the context of the Drivechain proposal, for UTXOs in miner-controlled escrows to be spent, they should be voted on by every block over a lot of blocks, proper?

Now, how are these votes made and the place are they computed? I believe the votes are someway written within the block coinbase, however how precisely? It is not like there’s a lot area there. After which every full node has to maintain a desk of what transaction has what number of votes and confirm towards that at any time when a transaction is included within the block?