NOLAYER - alternative text for layers
Content that is surrounded by <NOLAYER>
and </NOLAYER> tags is
displayed by browsers that do not support the LAYER and ILAYER
tags. This content is ignored by browsers that do support these
tags. Therefore, you can use the NOLAYER tag to display content in
browsers that will not support the LAYER and ILAYER tags.
Note, however, that browsers that do not support the LAYER and
ILAYER tags will display content inside these tags, but the
browsers will ignore all positioning information and will lay all
the content out sequentially. You could use the SRC attribute to
specify positioned content that is stored in a separate file, and
then use the NOLAYER tag to display an advisory message to users
that they need a LAYER-enabled browser to view the page.