URL without "http|https"
Protocol relative URL
You may receive unusual security warnings in some browsers.
See also, Wikipedia Protocol-relative URLs for a brief definition.
At one time, it was recommended; but going forward, it should be avoided.
See also the Stack Overflow question Why use protocol-relative URLs at all?.
It is called network-path reference (the part that is missing is called scheme
or protocol
) defined in RFC3986 Section 4.2
4.2 Relative Reference
A relative reference takes advantage of the hierarchical syntax (Section 1.2.3) to express a URI reference relative to the name space of another hierarchical URI.
relative-ref = relative-part [ "?" query ] [ "#" fragment ] relative-part = "//" authority path-abempty / path-absolute / path-noscheme / path-empty
The URI referred to by a relative reference, also known as the target URI, is obtained by applying the reference resolution algorithm of Section 5.
A relative reference that begins with two slash characters is termed a network-path reference (emphasis mine); such references are rarely used. A relative reference that begins with a single slash character is termed an absolute-path reference. A relative reference that does not begin with a slash character is termed a relative-path reference.
A path segment that contains a colon character (e.g., "this:that") cannot be used as the first segment of a relative-path reference, as it would be mistaken for a scheme name. Such a segment must be preceded by a dot-segment (e.g., "./this:that") to make a relative- path reference.