The positioning elements in HTML were introduced by Netscape to
allow an author to define precisely positioned, 2-dimensional
layout consisting of overlapping layers of transparent or
solid content on a web page. Content of these positioning mechanisms
can be treated as a single item of content that can be moved and
altered in various ways.
Support
These elements are curious in that it mirrors almost all of the functionality
and capabilities now offered through the
Style
Sheet Positioning[-->Index DOT Css] properties.
for Cascading
Style Sheets. The LAYER and ILAYER elements are essentially
HTML-based solutions to the same functionality that these CSS properties
provide. It is interesting to note that support for CSS positioning and
the LAYER/ILAYER elements appeared in Netscape at the same time (4.x.) However,
CSS positioning has been created with the official sanctioning of the W3C,
and Netscape itself has abandoned support for these elements after 4.x.
Hence, use of these elements is NOT recommended.
This element indicates an "in-line" layer. If no positioning is
specified, the layer will appear within the flow of a document (behaving
like an IMG element.) If positioning values ARE used on this type
of layer, the positioning coordinates are relative to where the layer
would ordinarily occur in the document flow.
Layer:
This type of layer is also known as an "out-of-flow" or
"positioned" layer. It is used to define explicit positioning
of a block of content.
Nolayer:
This element is used to mark a section of document content for display
only for backward compatibility purposes. Browsers that understand HTML
positioning elements will ignore this and non-supporting browsers will
render it. It may also be applicable when non-conforming browsers try to
render layered pages that include these elements using the SRC attribute.
In such a case, older browsers would not be able to access the referenced
sub-document, so this element becomes a necessary fallback.