Based on the spec ( http://www.w3.org/TR/html5/document-metadata.html#the-link-element http://www.w3.org/TR/html5/document-metadata.html#the-link-e... ) requiri

Based on the spec ( http://www.w3.org/TR/html5/document-metadata.html#the-link-element http://www.w3.org/TR/html5/document-metadata.html#the-link-e... ) requiring a valid URL ( http://www.w3.org/TR/html5/infrastructure.html#valid-url http://www.w3.org/TR/html5/infrastructure.html#valid-url ) it would interpret it as a relative link to a path "fonts.googleapis.com" if you didn't specify '//' to indicate it was absolute. I don't agree that the spec should make an exception when rel is "dns-prefetch" and consider all href tags to be FQDNs or similar.