XHTML 1.0

Semantically equivalent to HTML 4.01
Uses XML syntax
Has been carefully designed to make use of "quirks" of existing HTML browsers
Use a small number of guidelines, eg:
- All elements must be closed (eg, <p>...</p>
- All attribute values must be quoted
- Use space before "/" of empty elements: <hr />
- ...
Resulting documents can be served both as XML and HTML documents