A recent tweet from Google’s Gary Illyes called attention to problem of invalid HTML. Google is fine with invalid HTML. Less well known is that there are negative outcomes associated with invalid HTML ...

Some might not know this, but it’s always a good idea for web administrators to check websites for any form of problems in a bid to make sure end users are safe from external harm whenever they visit.

While a well-formed document is well-formed because it follows rules defined by the XML spec, a valid document is valid because it matches its document type definition (DTD). The DTD is the grammar ...