| HTML 4.01 |
XHTML 1.0 |
| Forgiving |
Requires discipline and attention to detail |
| Correct nesting required in theory |
Correct nesting absolutely required |
| Some end tags optional |
All end tags required |
| No end tag for empty content model |
Even empty content model requires end tag |
| Case insensitive |
Lowercase only |
| Some attribute values needn't be quoted |
All attribute values must be quoted |
| Certain "valueless" attribute values are OK |
All attributes must have values |
| Less sensitive to special characters |
More sensitive to special characters |
| Ubiquitous name attribute |
Id attribute preferred to name, mostly |
