A layer is a container for HTML content, usually delineated by the DIV or SPAN tag, that you can position anywhere on a page. Layers can contain text, images, forms, plug-in objects, and even other layers—any element you can place in the body of an HTML document you can also place in a layer.
Layers provide Web page designers fine control over the exact pixel placement of elements. By putting page elements in layers, you can control which objects appear in front of each other and which ones are displaced or hidden. You can also use a timeline to move a layer or several layers simultaneously across a screen.
In Dreamweaver you can use two layer formats for positioning content on a page: CSS layers and Netscape layers.
 |
CSS layers (also known as CSS-P elements) position content on a page using the DIV and SPAN tags. The properties of CSS layers are defined by the World Wide Web Consortium's Positioning HTML Elements with Cascading Style Sheets. |
|
Netscape layers position content on a page using the Netscape LAYER and ILAYER tags. The properties of Netscape layers are defined by Netscape's proprietary layer format. |
Both Internet Explorer 4.0 and Netscape Navigator 4.0 support layers created using the DIV and SPAN tags. Only Navigator supports layers created with the LAYER and ILAYER tags. Earlier versions of both browsers will display the contents of a layer but will not position them.
Positioning properties for layers include left and top (x and y coordinates, respectively), z-index (also called the stacking order), and visibility. Positioned elements can be defined with the DIV, SPAN, LAYER, and ILAYER tags in Dreamweaver. See Layer preferences.