HTML Checking for Large Sites

Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.

The “sizes” attribute may be specified only if the “srcset” attribute is also present.

The sizes attribute is used to complement the srcset attribute on an <img> tag for responsive images, therefore it’s not valid if srcset is missing. Check the HTMLImageElement.srcset guide to learn about the correct usage of the srcset and sizes attributes.

Related W3C validator issues