[1] Though W3C validation is important for browser compatibility and site usability, it has not been confirmed what effect it has on search engine optimization.
As HTML5 has removed the use of DTD in favor of a "Living Standard", the traditional Markup Validation Service is not applicable to these formats.
[1] It was developed to be a more intuitive version of the first online HTML validator written by Dan Connolly and Mark Gaither, which was announced on July 13, 1994.
[6] Many major web browsers are often tolerant of certain types of error, and may display a document successfully even if it is not syntactically correct.
Mark-up validators cannot see the "big picture" on a web page,[clarification needed] but they excel at picking up missed closing tags and other technicalities.