Yeah I know. Hence mentioning record types in the question you're reponding to. But yes, that wikipedia page has some info:
> WKS: Record to describe well-known services supported by a host. Not used in practice. The current recommendation and practice is to determine whether a service is supported on an IP address by trying to connect to it. SMTP is even prohibited from using WKS records in MX processing.[12]
Can't find any reference to WKS as a 'field' or record type. Any greybeards want to elaborate?