HTML Checking for Large Sites
Rocket Validator automatically scans your sites for accessibility issues using the W3C Validator,
hosted on our own servers and integrated into our web crawler.
Bad value X for attribute “height” on element “iframe”: Expected a digit but saw “%” instead.
The <iframe> element, used to embed another document inside the current document, accepts both attributes width and height which must be valid non-negative integers. Percentages are not allowed for these attributes.
Check https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-iframe-element.