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| Tag | Attribute | 2.0 | 3.0 | 3.2 | 4.0 | Internet Explorer |
Mosaic | Netscape | Opera | |
|---|---|---|---|---|---|---|---|---|---|---|
| <!-- --> | X | X | X | X | 1.0 | 1.0 | 1.0 | 2.1 | ||
| <!Doctype> | X | X | X | X | -- | -- | -- | -- | ||
| <![Downlevel-Hidden Block]> |
-- | -- | -- | -- | 5.0 | -- | -- | -- | ||
| <![Downlevel-Revealed Block]> |
-- | -- | -- | -- | 5.0 | -- | -- | -- | ||