Rollover

Rollover is a widely used dHTML effect, its name originally coming from Macromedia Director's scripting language, Lingo. Internet Explorer 4.0 first supported rollover effects through Cascading Stylesheets (CSS) without requiring extra code. The dHTML mouseover works by switching the visibility of a CSS layer from hidden to visible and back again. This kind of rollover allows you to swap in text or plug-ins, as well as alternate back and forth between images to create the effect. The 4.0 implementation of CSS and JavaScript is not consistent, however, so the code can get ugly.