The CSShark Answers FAQs site has some good information on using precisely this recipe to make a site work in both NN4.x and more modern browsers. It has plenty of tips and tricks and mentions the common pitfalls that can break cross-browser compliance. I usually have a browser window open to the site when I'm designing a new layout.

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$rattusillegitimus = Eliza::PerlMonks::Robot::new()