Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.
HTML issues tagged as number.
The boolean required attribute can only be used with certain types of inputs. Check the input type is one of the allowed.
The required attribute, if present, indicates that the user must specify a value for the input before the owning form can be submitted.
When was the last time you validated your whole site?
Keep your sites healthy checking for A11Y/HTML issues on an automated schedule.