Re: B.2 DTD required or optional?

Tim Bray wrote:
> At 03:05 PM 10/12/96 CDT, Michael Sperberg-McQueen wrote:
> >B.2 Should XML require each document instance to have a DTD or not
> >(7.1)?
> One concept is that the XML spec should define two separate characteristics
> that a document can have, well-formedness and validity.
> A. A "Well-Formed XML Document" has
> 1. syntactically distinguishable elements, attributes, comments, and PI's
> 2. one root element
> 3. all elements properly nested within each other
> 4. no text outside the root element
> Such a document may or may not contain markup declarations.  If it does,
> well-formedness also allows
> 5. empty elements, if they're declared
> 6. entity references, if they're declared
> B. A "Valid XML document" means there's a full DTD and it's been validated
>    in the familiar SGML sense.

Why does an XML document require a single root?