[BIP Draft] Co-signer Spending Policies

A policy hash must encapsulate the precise semantics of the verifier, rather than just referencing a syntactically valid document. This involves explicitly defining the handling of unknown fields, the treatment of duplicate keys, and whether default values are mandated to be explicit. Without such specificity, there exists a risk that different implementations could interpret identical input bytes differently, potentially enforcing divergent conditions.

The format chosen for encoding, such as JSON or TLV, is a distinct concern from semantic commitment. Ensuring consistency in verification requires that the policy commitment is domain-separated from both statement and transaction hashes. Additionally, it is advisable to incorporate the format version directly into the preimage of the hash to further guarantee unambiguous interpretation across different implementations.