Microsoft Internet Explorer controls them with style sheets. Layers aren't just for page designers. Users can also manipulate them. Layers can be hidden or shown and can change over time based on user input or some other condition. They can even be set in motion to create animation-like effects.
Layers can hold images, text, frames, or any other sort of element.
A layer's clipping area can be adjusted to show part of a layer at a time, slowly reveal the layer to the user, or slowly make it disappear. You can accomplish all of these tricks with a simple set of attributes. A style sheet is a standard format all pages on a site follow for colors, fonts, margins, and other layout details. Users can also create style sheets for their browsers, so every page they visit has the same look. Even with CSS, users can still dictate how pages look in their browsers by setting preferences.