Icons! We see them all over the web, and they're essential to most pattern libraries and web design systems. I recently needed to implement such a system. It had to be non-prescriptive, scalable, and dynamically editable via CSS. The icons were to be used by multiple teams in many different applications, built with various frameworks and techniques. They needed to have the ability to be restyled, get cached, and be updated quickly and easily as more icons are added. Basically, the icon system needed to be really, really flexible. Challenge accepted.