9.3. Conclusion

This is one of the few rules that addresses performance of the page after it has been loaded, which is generally when CSS expressions cause problems. However, in some cases, CSS expressions can affect the load time of a page, too. One property at Yahoo! had a CSS expression that caused a 20-second delay during the initial rendering of the page. This result was unexpected and took a while to diagnose. Similarly, who would have thought the CSS expression used in the "Expression Counter" example would cause Internet Explorer to lock up if the user clicked in a text field? A full discussion of complicated CSS incompatibilities, such as min-width and position: fixed, is beyond the scope of this book, and that's the point—using CSS expressions without a deep understanding of the underlying implications is dangerous.

Avoid CSS expressions.