PKIX is the Internet's PKI as specified by the Internet Engineering Task Force (IETF). PKIX details X509 certificate formats, issuing rules and validation rules.
PKIX is the Internet's PKI as specified by the Internet Engineering Task Force (IETF). PKIX details X509 certificate formats, issuing rules and validation rules in various Request for Comments (RFC).
Not all PKI's are PKIX. Organizations and government agencies can run a private PKI with rules that are different from PKIX. The documentation and rules for the US government's PKI is over 2000 pages.
User agents such as browsers use a different set of issuing policies than those specified in the RFCs. The browser issuing polices are provided by the CA/Browser Forum (CA/B Forum), and explains why browsers reject certificates that OpenSSL, Wget and other free software accept.