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| HTML | XHTML | Browsers | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tag | Attribute | 2.0 | 3.0 | 3.2 | 4.0 | 1.0 | 1.1 | IExplorer | Mosaic | Netscape | Opera | ||
| <!-- --> | X | X | X | X | X | X | 1.0 | 1.0 | 1.0 | 2.1 | |||
| <!DOCTYPE> | X | X | X | X | X | X | 6.0 | -- | 6.0 | 7.0 | |||
| <![Downlevel-Hidden Block]> | -- | -- | -- | -- | -- | -- | 5.0 | -- | -- | -- | |||
| <![Downlevel-Revealed Block]> | -- | -- | -- | -- | -- | -- | 5.0 | -- | -- | -- | |||