//example.com/img.png is a perfectly valid URI syntax as per RFC 3986: Section 4.2. It is relative to the current scheme, and therefore as you mentioned, it can be very useful when switching between HTTP and HTTPS, because you won’t need to explicitly specify the scheme. All modern browsers will understand that format, including IE 6. … Read more
is this URL format safe to use for all browsers. I can’t say anything for sure, but you should be able to test it in different browsers. And is it a standard? Technically, it is called “network path reference” according to RFC 3986. Here is the scheme for it: relative-ref = relative-part [ “?” query … Read more
The resource you’re looking for is the RFC 3986. See Section 4.2 and Section 5.4. Quoting from the latter: Reference Resolution Examples Within a representation with a well defined base URI of: http://a/b/c/d;p?q a relative reference is transformed to its target URI as follows: “g:h” = “g:h” “g” = “http://a/b/c/g” “./g” = “http://a/b/c/g” “g/” = … Read more
The question of whether one could change all their links to be protocol-relative may be moot, considering the question of whether one should do so. According to Paul Irish: 2014.12.17: Now that SSL is encouraged for everyone and doesn’t have performance concerns, this technique is now an anti-pattern. If the asset you need is available … Read more
A relative URL without a scheme (http: or https:) is valid, per RFC 3986: “Uniform Resource Identifier (URI): Generic Syntax”, Section 4.2. If a client chokes on it, then it’s the client’s fault because they’re not complying with the URI syntax specified in the RFC. Your example is valid and should work. I’ve used that … Read more