-/// Enforces some rules on ChannelKeys calls. Eventually we will probably want to expose a variant
-/// of this which would essentially be what you'd want to run on a hardware wallet.
+/// Initial value for revoked commitment downward counter
+pub const INITIAL_REVOKED_COMMITMENT_NUMBER: u64 = 1 << 48;
+
+/// An implementation of Sign that enforces some policy checks. The current checks
+/// are an incomplete set. They include:
+///
+/// - When signing, the holder transaction has not been revoked
+/// - When revoking, the holder transaction has not been signed
+/// - The holder commitment number is monotonic and without gaps
+/// - The counterparty commitment number is monotonic and without gaps
+/// - The pre-derived keys and pre-built transaction in CommitmentTransaction were correctly built
+///
+/// Eventually we will probably want to expose a variant of this which would essentially
+/// be what you'd want to run on a hardware wallet.
+///
+/// Note that before we do so we should ensure its serialization format has backwards- and
+/// forwards-compatibility prefix/suffixes!