HTML Checking for Large Sites
Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.
HTML issues tagged as iso code.
Bad value X for attribute “lang” on element “html”: The language subtag X is not a valid ISO language part of a language tag.
The specified language code in the lang attribute of the <html> tag is not a valid ISO code.
When was the last time you validated your whole site?
Keep your sites healthy checking for A11Y/HTML issues on an automated schedule.