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   Re: Why namespaces?

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  • From: Paul Prescod <paul@prescod.net>
  • To: XML-Dev Mailing list <xml-dev@ic.ac.uk>
  • Date: Sun, 29 Aug 1999 17:44:40 -0400

> Who said that they cannot be mixed?  

The XHTML specification: "Future work by W3C will address ways to
specify conformance for documents involving multiple namespaces."

> XHTML documents cannot (yet)
> contain markup from other Namespaces, but anyone else designing a
> document type is free to include HTML markup in theirs (say, for
> documentation in a schema).

What is the point of referencing a specification if you cannot define
conformance? I would say that it is downright a bad idea to "mix in"
HTML until there are rules for what is legal or not legal in doing so.
Right now, this is perfectly legal:

<book xmlns='urn:loc.gov:books'
       xmlns:isbn='urn:ISBN:0-395-36341-6' xml:lang="en" lang="en">
  <title>Cheaper by the Dozen</title>
  <!-- make HTML the default namespace for a hypertext commentary -->
  <p xmlns='http://www.w3.org/TR/xhtml1/strict'>
This is <title>also <table>available <a
 </table>.... </title>.

I personally don't think that the XHTML specification should even
mention the possibility of mixing in without defining contraints or

> In fact, without a global naming scheme, I cannot even reliably answer
> the following question for an arbitrary XML document (say, text/xml):
>   "Is this an HTML document?"
> The DOCTYPE declaration doesn't help at all here, as Eliot has
> repeatedly (and convincingly) pointed out -- DTDs are for
> guided-authoring and for validation, not for recognition.

It helps to the exactly the same degree that the namespace declaration
does. You aren't supposed to use the XHTML doctype on a document that
isn't HTML. That can't be checked entirely by any software short of a
full HTML validator but that's not the point: it's a societal/legal
declaration, not something computer-checkable.

That's exactly the same case with namespaces. There is no off-the-shelf
software that can check that a document "conforms" to the rules of its
namespace (if indeed there are any such rules). Unfortunatley, proper
use of either XHTML declaration must be enforced in courts, not

 Paul Prescod

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