HTML & XHTML: The Definitive Guide, 5th Edition

Layers

Spacers and multiple columns are natural extensions to conventional HTML, existing within a document’s normal flow. With Version 4, Netscape took HTML into an entirely new dimension with layers. It transforms the single-element document model into one containing many layered elements that are combined to form the final document. Regrettably, layers are not supported by Netscape 6 or any version of Internet Explorer.

Layers supply the layout artist with a most critical element missing in standard HTML: absolute positioning of content within the browser window. Layers let you define a self-contained unit of HTML content that can be positioned anywhere in the browser window, placed above or below other layers, and made to appear and disappear as you desire. Document layouts that were impossible with conventional HTML are trivial with layers.

If you think of your document as a sheet of paper, layers are like sheets of clear plastic placed on top of your document. For each layer, you define the content of the layer, its position relative to the base document, and the order in which it is placed on the document. Layers can be transparent or opaque, visible or hidden, providing an endless combination of layout options.

The <layer> Tag (Antiquated)

Each HTML document content layer is defined with the <layer> tag. A layer can be thought of as a miniature HTML document whose content is defined between the <layer> and </layer> tags. Alternatively, the content of the layer can be retrieved ...