为什么所有浏览器都下载所有CSS文件 - 即使是他们不支持的媒体类型？ [英] Why do all browsers download all CSS files - even for media types they don't support?

问题描述

如果我指定一个不支持的媒体类型（bork）的CSS链接，它仍然会被我试过的每个浏览器下载（包括桌面和几个移动浏览器）。

 < link href =bork.cssmedia =bork =stylesheettype = text / css/> 
  

并且变得更糟...

如果文件bork.css @import 是第二个CSS文件也被下载的其他CSS文件（也包含不支持的媒体类型）。

  / *内部bork.css* / 
 @import url（bork2.css）bork，博克
  

为什么？

某些浏览器可能正在搜索它们支持的媒体类型的嵌套 @import s或 @media 然后应用这些文件中包含的样式规则...

  / *在bork2.css* / 
 @import url（all.css）; 
 @media all {
 / * rules * / 
} 
  

...但是到目前为止我可以告诉，不是一个单一的浏览器。 （幸运的是，这将是一个错误。）

因此，所有这些下载似乎完全多余 - 除非有一些我一直错过的解释。

编辑：我想要了解的是激励浏览器制造商去：

嘿！让我们下载一堆CSS文件，我们没有打算申请，并停止加载其他资源同时！

我认为答案是这样的：

浏览器允许并鼓励解析 / code>描述符 - 无论是什么描述符 - 作为一种方式使它们变得友好

未来版本的HTML可能引入
新值，并允许参数化
值。

* From：http://www.w3.org/TR/html4/types.html#h-6.13

这样，媒体可能有一天包括 3d眼镜或其他描述符，包括 bork ; - ）

EDIT：

在媒体查询中说，这在一定程度上支持上述内容：

未知媒体
类型计算为false。有效地，
他们被视为与设备的
媒体类型不匹配的已知
媒体类型相同。

*：： http://dev.w3.org/csswg/css3- mediaqueries /＃error-handling

因此，它们被视为已知且已下载以供使用，而不是当时/用于该设备。

If I specify a CSS link with an unsupported media type ("bork") it still gets downloaded by every browser I've tried (including both desktop and several mobile browsers).

<link href="bork.css" media="bork" rel="stylesheet" type="text/css" />

And it gets worse...

If the file bork.css @imports an other CSS file (also with an unsupported media type) that second CSS file also gets downloaded.

/* Inside "bork.css" */
@import url("bork2.css") bork, bork;

Why!?

My first assumption was that some browsers might be searching for nested @imports or @media blocks with media types that they supported - and then apply the styling rules contained within those files...

/* Inside "bork2.css" */
@import url("all.css");
@media all {
  /* rules */
}

...but as far s I can tell, not a single browser does that. (Fortunately, as that would be a bug.)

So all this downloading seems wholly redundant - unless there's some explanation that I've missed all along.

EDIT: What I'm trying to understand is that motivates browser makers to go:
"Hey! We're trying to make our browser crazy fast! Let's download a bunch of CSS files that we have no intention of applying, and halt the loading of other resources meanwhile!"

解决方案

I think the answer is this:

Browsers are allowed and encouraged to parse media descriptors - no matter what the descriptor - as a way to make them future friendly

Future versions of HTML may introduce new values and may allow parameterized values.

*From: http://www.w3.org/TR/html4/types.html#h-6.13

In this way, media may one day include 3d-glasses or other descriptors, including bork ;-)

EDIT:

The latest CSS3 spec on media queries says this, which supports the above, to a certain degree:

Unknown media types evaluate to false. Effectively, they are treated identically to known media types that do not match the media type of the device.

*From: http://dev.w3.org/csswg/css3-mediaqueries/#error-handling

So they are treated as known and downloaded to be used, just not at that time/for that device.

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