We are developing a web application that will be sold to many clients. There is already one client (a bank) which has decided that it will buy the product once it is ready. Unfortunately due to some miscommunication it came out rather late that the only browser they use is IE6. The application was already started with the thought in mind that it does not need to support anything else below IE7. The results are pretty good too - it's fully useable on IE7/FF/Opera/Safari. Haven't tested on Chrome, but expect little problems there. Unfortunately there is now the IE6 requirement after all...
The application isn't too far developed yet, and the design is pretty much OK, so the change isn't that horrible. Still, it'll take some work.
A nice thing about IE6 is that it supports two nonstandard and very helpful features. First is conditional comments, which lets me include some CSS/JS files only for IE6. Second is CSS expressions. That is, things like this:
input
{
background-color: expression(this.type='text'?'silver':'');
}
In essence it binds CSS values to JavaScript expressions. This allows to easily emulate many CSS features that IE6 does not support natively, and could lighten my burden considerably.
Unfortunately IE is infamous for its JavaScript performance. I'm worried that using too many of these expressions might slow it down to a crawl. I also have no idea what computers the bank is using. Since it's a pretty big one, I'd expect a wide variety in all their branch offices. I don't expect to use anything much there - some simple math, ternary operators and looking at this element's/parent element's properties. Still there would be a couple dozen of these in the IE6_override.CSS file.
Can this be a problem?
Added: Blah, this was what I was afraid of. OK, will see how much I can use other hacks to get around the shortcomings. Thanx, people!
https://developer.yahoo.com/blogs/ydn/high-performance-sites-rule-7-avoid-css-expressions-7202.html
Turns out you might want to avoid using these, they are dangerous.