Starting external links to sites with "//"

Question

Possible duplicate:
Is it valid to replace with // in a <script src = "...">?
Links begin with two abbreviations

I have seen this on several sites. A simple example is to view the source of the Wikipedia landing page:

<link rel="shortcut icon" href="//en.wikipedia.org/favicon.ico" />
<link rel="apple-touch-icon" href="//upload.wikimedia.org/wikipedia/commons/f/f1/Wikipedia-mobile-icon.png" />
<link rel="copyright" href="//creativecommons.org/licenses/by-sa/3.0/" />

Is there any standard with starting external links from //? Is it just not to download extra ones https?:and save some characters, because most browsers are smart enough to add the rest of the circuit to their account? Or is this a legitimate thing, maybe for some other reason?

Answer 1

URL-, , , , , . , URL https, , //, https, http.

, , - IE, , , .

:

• URL-,

Answer 2

http https; , .

Answer 3

URL-, . :

http://paulirish.com/2010/the-protocol-relative-url/

:

HTTPS, HTTPS, * HTTP. " , " IE, .

...

When using in <link>or @importfor the IE7 and IE8 stylesheet, download the file twice. However, all other uses are very good.

... but overall you can use it safely.