CSS Expressions are no more in IE 8!

Posted by jcargoo | Tuesday, October 21, 2008
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With some hesitancy or may be confusion I have learned that the CSS expressions are no longer supported in IE8 standards mode, I mean when I read in ajaxian this post:

The CSS expressions of old will no longer work in IE 8. Whenever a feature goes away in IE, Ajax hackers get worried, as many hacks rely on quirks or proprietary features of the browser.
In the IEBlog here is what was exactly said:

Why end support for expressions?
  • To comply with standards
  1. Expressions are proprietary to Internet Explorer and as such not interoperable.
  2. A common use-case for expressions was to fix IE bugs or to emulate those CSS 2.1 features not yet supported by the browser, for example, min-width and max-width. We have not only worked hard to fix these bugs in IE8 but our new layout engine supports the missing features natively.
  • To improve performance
  1. Expressions evaluation has a high runtime cost; web performance experts like Steve Souders recommend avoiding them to improve front-end performance
  • To reduce the browser attack surface
  1. Because they expose a script execution context, CSS expressions constitute a possible script injection attack vector.
Are expressions still available in IE7 and Quirks mode ?
  • Yes. For backward compatibility, CSS expressions are still executed in Quirks and IE7 Strict modes. But starting with IE8 Beta 2, they are ignored in IE8 Standards mode.
Now it is real that for CSS 2.1 users the time will be convenient to finally have a full support browser of their version without checking/validating every time their CSS code under IE6. But the question is what the negative impact we really have?

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