The specification is at [ http://www.w3.org/TR/2000/REC-xhtml1-20000126/ ]

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If I understand XML correctly the main changes will be that

1. (1) All tags will have lower-case identifiers,
2. (2) There will be no optional omitting of end tags from certain structures like <p> and <br>,
   (3)Endless tags will have the XML format <img ...../> or <br></br>.
   (4)An attribute like ISMAP must be written like this ismap="ismap"
3. (5)All attribute values must be quoted.
   (6) An id attribute will be used instead of name.

Glossary