Performance and RFC 2396
Post from February 18, 2009 (ā» June 10, 2021), filed under Web Development.
This and many other posts are also available as a pretty, well-behaved ebook: On Web Development.
RFC 2396 specifies that relative URIs like //foo
get resolved as http://foo
. This means, if you link a resource like https://example.com/
, @href
may as well just point to //example.com/
.

Figure: An image that wouldnāt be there if @src
couldnāt start with //
.
This has two advantages: You can avoid security alerts when juggling with and switching between http and https, and you can save a couple of characters per URI reference. But Iām saying that just to inspire performance critics who already and with great joy discussed general advantages of HTML, including omitting optional tags.
Since this part of RFC 2396, seen as a whole, is still relatively new to me feel free to add to this. Iām just curious and love experimenting. So after I verified that all major browsers support the //
syntax I actually created a āhoneypotā test page to see whether that page gets indexed properly by search engines. Watch this space for the findings.
Update (February 28, 2009)
As it seems, all major search engines followed the āhiddenā links to the RFC 2396/3986 test page I set up: Google was first, Yahoo, Microsoftās Live Search, and Altavista followed over the last days. Thereās a slim chance that the test might have been compromised, but there are no indicators whatsoever solidifying that concern.
Update (June 28, 2013)
Weāve found this approach so useful, itās common practice now.
About Me

Iām Jens Oliver Meiert, and Iām an engineering manager and author. Iāve worked as a technical lead for Google, Iām close to the W3C and the WHATWG, and I write and review books for OāReilly. Other than that, I love trying things, sometimes including philosophy, art, and adventure. Here on meiert.com I share some of my views and experiences.
If you have questions or suggestions about what I write, please leave a comment (if available) or a message.
Comments (Closed)
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On February 18, 2009, 11:09 CET, Kroc Camen said:
Most excellent, I really look forward to your findings. This syntax will be especially pertinent to the regex I use for publishing.
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On February 18, 2009, 21:49 CET, potherca said:
I come from a back-end development background myself and for the last year or so Iāve been delving deeper and deeper into the front-end. This is one of those fun little quirks I really enjoy to encounter⦠Just thinking out loud here, but I wonder how this compliments/collides with (for example) user-input validation?
Looking explicitly for ahttp://
isnāt necessary⦠things could be greatly simplified. Links only need to be/
(on-site) or//
(off-site).What fun š
Like the right honorable K. Camen, I to am looking forward to your findings⦠Keep us informed!
-
On February 18, 2009, 23:36 CET, Keith Bell said:
Jens, I wasnāt aware of that before. Itās interesting in a āmaybe Iāll find a use for that one dayā kind of way.
I wonder if the syntax is supported well by mobile user agents.
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On February 19, 2009, 9:12 CET, Francesco said:
Thatās pretty interesting! Iām looking always for ways to trim my code as much as possible. Looking foward to your results!
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On February 23, 2009, 9:57 CET, Gunnar Bittersmann said:
Why do you refer to RFC 2396 which has been obsoleted by RFC 3986 for 4 years?
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On February 23, 2009, 10:03 CET, Jens Oliver Meiert said:
Gunnar, maybe because RFCs just state what they make obsolete, not by what they became obsolete. Thanks for the reference.
Letās call this post āPerformance and RFC 2396/3986ā then š
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On February 23, 2009, 16:51 CET, Gunnar Bittersmann said:
Hm, funny. The HTML version of RFC 2396 lists āObsoleted by: 3986ā and āUpdated by: 2732ā; the plain text version does not.
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On April 15, 2009, 20:29 CEST, Steven Black said:
Works in IE and Firefox. But Chrome resolves ā//ā as āfile://ā.
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