W3C has a candidate proposal for specifying the rules for the id="" attribute.

http://www.w3.org/TR/2005/PR-xml-id-20050712/

Note how it says that W3C "licenses" the attribute "xml:id" for this purpose. Apparently, the purpose of this document is to more cleanly separate xml:id from other types of attribute. This will likely add the ID type to the DOM spec, as attributes are Nodes, too.

This probably won't affect how we use the id attribute, but it is an interesting read, and might help with decisions on how we use it.

Bob