[michaelw]

CSS Expressions. Aka Dynamic Properties.

Recently deprecated http://msdn.microsoft.com/en-us/library/ms537634(VS.85).aspx

Ironically now showing up in other browsers own extensions.

Reasons for failure:

* distrust of Microsoft inventions in the browser

* incomplete implementation strategy based on javascript instead of custom expression parser

* security issues because of using javascript instead of a custom expression parser

[flomo]

FWIW, these were used quite a bit back in the dark-ages.

Always thought of them as a halfway point between pure CSS and Netscape's idea of implementing stylesheets in Javascript.

[superk]

Add to the failure list:

* Terrible performance - practically first rule for optimizing page rendering is "don't use CSS expressions"

http://code.google.com/speed/page-speed/docs/rendering.html http://developer.yahoo.net/blog/archives/2007/07/high_perfor...

* Only work on IE natch.

So, you have Javascript which was better performance and worked everywhere.

I think it's a little misleading to say it's the best feature no one ever used. CSS expressions were re-born as hardware-accelerated CSS3 transitions - with a much better, more focused implementation, and are pretty popular these days - especially for mobile.