There are six tags that are only visible with Netscape. Keep in mind that many of these tags (such as <layer></layer>) are not a part of the XHTML specification.
The text within the <blink></blink> tag will turn on and off (blink). This can make text fairly difficult to read. This tag works in both Netscape and Mozilla.
This tag was meant to generate a public key to encrypt HTML forms and make them secure. It works in Netscape and Opera.
The layer tag allows you to place sections of your Web page on different "layers" and treat them as separate objects within your page. Use of this tag is discouraged in favor of CSS positioning. This only works in Netscape 4.x.
The enclosed text will be displayed in multiple columns. This tag was meant to be used to create newspaper-like columns of text. This works in Netscape 4.x.
The <nolayer></nolayer> tag indicates HTML that should be displayed in browsers that don't support the <layer></layer> tag, when layers are used. It is similar to the <noframes></noframes> tag in a frameset.
The spacer tag was Netscape's take on the non-breaking space. Use this tag to put a specific sized block of white space on your Web page. Note that this tag works in the Netscape 4 and 6.