W3C home > Mailing lists > Public > public-html@w3.org > December 2010

Re: what to do with invalid (or improper) mime-type resources

From: Aryeh Gregor <Simetrical+w3c@gmail.com>
Date: Sat, 18 Dec 2010 18:12:48 -0500
Message-ID: <AANLkTin6E1q-ZNuB+E8GU4uP4xjTnq5ziaz7dtH_SOx7@mail.gmail.com>
To: Getify <getify@gmail.com>
Cc: public html <public-html@w3.org>
On Fri, Dec 17, 2010 at 7:18 PM, Getify <getify@gmail.com> wrote:
> I'm also trying to interpret the "spirit" of the spec with respect to how
> the user-agent should behave if it actually requests a resource (because
> let's say the author omits the `type` attribute on the container) and the
> container which receives it cannot validly process the type. For instance,
> if `new Image()` (in JavaScript) is used to fetch a URL, or if <object> does
> the same, and the resource that's returned is actually a script (or CSS
> file), it seems clear that the spec says the element should be ignored.

That depends on exactly what context it's used in.  The spec is meant
to be written so you can figure out what the letter of the spec means,
without having to interpret the "spirit".  If it doesn't explicitly
say something, that behavior is undefined.

> But I'm curious if that means (or *should* mean) that the resource is
> discarded/purged from the cache (if it was cached)? Or should that element
> be left alone in the cache? Some browsers are in the habit of "marking" such
> "ignored" resources with the invalid type, thus tainting that resource from
> being properly used with its correct type at a later time in the page
> life-time.
> In other words, what is the full intent of "ignored"? Should the spec be
> clear about how such an element should be treated in the cache?

The spec is deliberately not specific about exactly how resources are
loaded and cached, because it's good for browsers to be able to
innovate and compete on the algorithms they use for this.  The
difference should not be black-box-detectable -- except for
performance, of course.

> I ask because many different "loaders" (both CSS and JavaScript) attempt to
> use <object> and `new Image()` to "preload" (that is, load into cache, but
> not parse/execute) such content.
> Is this a "safe" hack, or is it likely that such "preloading" will
> eventually (or is intended to be) prevented?

It sounds like a dedicated feature would be the desired way to solve
this.  I'm not sure offhand if one exists.  What's the reason for
using tricks to preload CSS or JS instead of just going ahead and
loading it normally?  Is it because of some inherent limitation, or
just because of poor existing implementations?  Recent browser
versions have gotten much smarter about fetching things in parallel
and so on -- is this stuff still needed for the latest browsers?
Received on Saturday, 18 December 2010 23:13:41 UTC

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