[Bug 1655461] w3c-markup-validator-21.10.12 is available

https://bugzilla.redhat.com/show_bug.cgi?id=1655461

--- Comment #34 from Sergio Basto  ---
to complete the information:
https://raymii.org/s/tutorials/Local_W3C_HTML5_Validator_Server.html
https://about.validator.nu/#api
https://validator.github.io/validator/#options and "Build instructions" chapter