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

Ian Hickson ian at hixie.ch
Thu Apr 28 12:42:40 PDT 2011

On Thu, 9 Dec 2010, Roger Hågensen wrote:
> 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.
> vs
> 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 general.
> 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.

You can basically already do all this by just encoding the 
last-modified-date into the URL and giving the file a huge expiry time. 
When the URL changes, the browser knows to fetch a new file.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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