Rocket Validator automatically checks your pages on the W3C Validator.
HTML issues tagged as inputmode.
inputmode attribute specifies what kind of input mechanism would be most helpful for users entering content into the form control. This attribute is not supported in all browsers, so it’s advised to use with caution and consider alternatives for older browsers.
When was the last time you validated your whole site?
Keep your sites healthy checking for A11Y/HTML issues on an automated schedule.