* [https://www.iso.org/standard/40874.html ISO-8601] International Organization for Standardization, "Data elements and interchange formats -- Information interchange -- Representation of dates and times”, ISO 8601:2004
* [https://web.archive.org/web/20070930181613/http://www.itu.int/ITU-T/publications/recs.html ITU-T509] International Telecommunication Union Telecommunication Standardization Sector (ITU-T), Recommendation X.509: Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks, May 2000. Specification and technical corrigenda -
* [https://web.archive.org/web/20160204203910/http://www.unix.org/version3/ieee_std.html POSIX ERE] The Open Group, Base Specifications Issue 6, IEEE Std 1003.1, 2004 Edition
