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 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.
H.3.1. 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 from another HTML document by using the src attribute with
the <layer> tag.
<layer> (Antiquated)
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Regardless of its origin, Netscape 4 formats a layer's content
exactly like a conventional document, except that the result is contained within
that separate layer, apart from the rest of your document. You control the
position and visibility of this layer using the attributes of the
<layer> tag.
Layers can be nested, too. Nested layers move with the
containing layer and are visible only if the containing layer itself is
visible.
