When you write Web pages, a good rule of thumb is to write pages that are accessible to as many browsers as possible. The W3C came up with accessibility guidelines that are easy to use.
There are three primary divisions of browser specific tags:
- Netscape only tags
- <blink></blink> (Netscape and Mozilla)
- <keygen></keygen> (Netscape and Opera)
- <layer></layer> (Netscape 4)
- <multicol></multicol> (Netscape 4)
- <nolayer></nolayer> (Netscape 4)
- <spacer /> (Netscape 4, 6)
- Internet Explorer only tags
- <bgsound />
- <marquee></marquee>
- MSNTV only tags
- <audioscope></audioscope>
- <blackface></blackface>
- <shadow></shadow>
- <sidebar></sidebar>
- XHTML 1.0 tags that aren't supported in any browser
- None, that I am aware of

