Why does the <link> ‘title’ attribute cause browsers to ignore my styles?_问答_开发者

Why does the <link> ‘title’ attribute cause browsers to ignore my styles?

开发者 https://www.devze.com 2022-12-15 06:35 出处：网络

The following html document (together with the CSS) fails to render the styles in b.css. <!doctype html>

相关专题：css

The following html document (together with the CSS) fails to render the styles in b.css.

<!doctype html>
<html>
    <head>
        <link rel="stylesheet" media="screen" type="te开发者_如何学Cxt/css" title="A" href="a.css" />
        <link rel="stylesheet" media="screen" type="text/css" title="B" href="b.css" />
    </head>
    <body>
        <div id="A">A</div>
        <div id="B">B</div>
    </body>
</html>

/* a.css */
div#A   { color: blue;  }
/* b.css */
div#B   { color: red;   }

Making the titles the same (e.g. both <link ... title="A"> fixes it, but I don't see the reason, why it should. What is the title doing, here, that makes this wrong?

The HTML spec states that there are three kinds of stylesheets: persistent, preferred, and alternate.

A stylesheet is "persistent" if it is linked with rel="stylesheet" and has no title attribute. All persistent stylesheets are used when rendering.
A stylesheet is "preferred" if it is linked with rel="stylesheet" and has a title attribute; preferred stylesheets with the same title are grouped together, but there should not be more than one group. It seems browsers will choose just one preferred stylesheet to render since there should be only one.
Finally, a stylesheet is "alternate" if it is linked with rel="alternate stylesheet" and has a title. These stylesheets are supposed to allow the user to choose stylesheets, they are grouped together by title and show up in the browser's stylesheet selector if it has one (View >> Page Style in Firefox). Each group (by title) is mutually exclusive.

By putting title attributes on your stylesheets, you're unwittingly making them into preferred stylesheets rather than the expected persistent stylesheet. This is also why they work when they all have the same title.

Following up on Neil Williams' answer:

Authors may specify a number of mutually exclusive style sheets called alternate style sheets.... User agents should allow users to select from alternate style sheets.

(emphasis added)

Also:

To make a style sheet preferred, set the rel attribute to "stylesheet" and name the style sheet with the title attribute.

This is from http://www.w3.org/TR/REC-html40/present/styles.html#h-14.3.1

Read this: http://blogs.telerik.com/dimodimov/posts/08-05-15/title_attributes_in_css_link_tags_prevent_styles_from_being_applied.aspx

I have been aware for some time now that title attributes in CSS tags trigger problems and prevent some CSS styles from being applied on the web page. Today I invested a couple of hours in finding out what actually happens and this is what we've got.

If you have several tags in the page and one of them has a title attribute, then the tags coming after it must either have a title attribute with the same value or no title attribute at all, otherwise the styles in the latter CSS files the will not be applied on the page.

The issue can be easily reproduced in various versions of Firefox, Opera and Safari. The only browser, which does not exhibit the unexpected behavior is Internet Explorer.