Rendering Mode and Doctype Switching

Rendering Mode and Doctype Switching: "Rendering Mode and Doctype Switching
By: Holly Bergevin

Even though today's browsers have moved toward more standards-compliant behavior, it is still necessary to allow older pages to display as they have in the past, regardless of proprietary features and invalid markup. However, this can cause problems with modern pages written to (x)HTML and CSS standards, especially if a browser cannot determine how to best render the page."