Of course, the humor here lies in the fact that IE has had dynamic CSS calculations since IE 5, but is now in the process of removing them – just as they are being standardized in other browsers.

For example [1]: <div style="left:expression(document.body.clientWidth/2-oDiv.offsetWidth/2);">Content</div>

These expressions (or "dynamic properties") essentially evaluated JScript embedded inside a stylesheet and provided some handy hacks to get around otherwise-painful bugs. This included simple math calculations as described in the Mozilla post, but also more complex transformations such as varying the style of an element based on the current day (or other JS-retrievable information).

Funny to see Mozilla phasing this in just as Microsoft phases something similar out [2].

[1] http://blogs.msdn.com/b/ie/archive/2008/10/16/ending-express...

[2] http://msdn.microsoft.com/en-us/library/ms537634(VS.85).aspx...