[whatwg] Proposal: add attributes etags & last-modified to <link> element.

Roger Hågensen rescator at emsai.net
Thu Dec 9 05:20:55 PST 2010

On 2010-12-08 20:44, Ian Hickson wrote:
> On Mon, 20 Sep 2010, Roger Hågensen wrote:
>> It would be better to define this as explicitly indicating which
>> resources are NOT valid any longer, with most sites/web applications
>> this would only be a select few links.
> Doing that would require knowing what the browser's cache contains.

Actually it would help the browser to display content faster and with 
less bandwidth use,
as the html document would have last-modified for <link> elements,
the browser then just checks if the linked element is cached and if it 
is, is the last-modified different.

While currently the browser would make a last-modifed http header 
request for the link element.
A <link> or <script> with a href is less likely to change than the html 
contents on the majority of sites,
so being able to hint to the browser that this css or that javascript 
was not changed saves the browser the (multiple) roundtrips to check if 
the last-modified of the css or js file.

So a last-modifed just lets the web author tell the browser cache that 
the link is stale or not stale.
So it's:
1. http header or http get of html, if not cached or stale or cache 
heuristics thinks that last-modified should be re-checked.
2. do the same with all hrefs, sources etc. in the html document.
1. same as 1 above but last-modified hinting of href and src allows the 
browser to skip step 2 (in well authored or well made template based 
pages obviously).

Damn. I think I skewed this whole topic away from it's original subject 
to last-modified being supported by all link/href/src etc. in html in 
Which may not be a bad idea really, as a last-modified="timestamp_here" 
(timestamp is http://www.ietf.org/rfc/rfc2822.txt )
would only be a few bytes vs a http header call or a full http get call 
and added to that the latency/delay in addition.
Shortening last-modified to modified might be something to consider as well.

Roger "Rescator" Hågensen.
Freelancer - http://www.EmSai.net/

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