This has been around for a very long time (2005 or so). They were originally called Persistent Identification Elements. Have a browse: http://duckduckgo.com?q

This has been around for a very long time (2005 or so). They were originally called Persistent Identification Elements. Have a browse: http://duckduckgo.com?q=persistent+identification+elements&v= http://duckduckgo.com?q=persistent+identification+elements&#...