Bitcoin Taproot Leaf Version: Future-Proofing Scripts
The leaf version field reserves space for new Bitcoin script rules without a hard fork, the exact mechanism, the constraints, and what it enables.
№ 002BitcoinBitcoin's Taproot Annex: Protocol Extensions Explained
The Taproot annex sits consensus-valid but relay-blocked inside every Taproot input, a reserved extension point whose format and uses are still being settled.