Certification Practice Statement
Some elements of a CPS include documenting practices of:
By detailing the practice of issuance, revocation and renewal, a CPS aids entities in judging the relative reliability of a given certificate authority.
Web of trust
Because individuals act as certifiers in a web of trust, individual CPS documents are sometimes used. For example, in a PGP WoT, the CPS might state that the certifying entity checked two forms of legal government ID before signing the person's public key.
When verifying digital signatures, it's necessary to review the CPS so as to determine the meaning of the issuance of the certificate by the certifying entity.