The spec says:
The rules for parsing XML documents (and thus XHTML documents) into DOM trees are covered by the XML and Namespaces in XML specifications, and are out of scope of this specification.
However, the spec says the following about the id attribute:
If the value is not the empty string, user agents must associate the element with the given value (exactly) for the purposes of ID matching (e.g. for selectors in CSS or for the getElementById() method in the DOM).
The second quote implies that the first quote is not the full story and building a DOM tree from an XHTML document byte stream is not entirely covered by the XML and Namespaces in XML specifications but there is a piece of code somewhere between the XML processor and the resulting DOM tree that is analogous to an xml:id processor and that assigns IDness to attributes that are not in a namespace, have the local name "id" and belong to elements in the XHTML namespace.
(When I started looking for spec justification for adding a filter that assigns IDness on the SAX level, I didn't find explicit justification--just the implicit justification from the second quote that seems to contradict a strict reading of the first quote.)
-- Henri Sivonen [EMAIL PROTECTED] http://hsivonen.iki.fi/
