[XML-SIG] DOM documentation update

[Martin v. Loewis]

> Yes, but how to use the IDL to document it without confusing the
> many non-IDL users who will be using the docs?
> 
> I'd rather we hjust add the type info where you point it out (and
> anywhere else), and link to the IDL for advanced users.

I don't think it would be confusing; most users should easily
comprehend the meaning of that notation without being formally
introduced into it. But I agree that putting an English text
describing the types would be also acceptable.

> > Incorrectly mentioned is namespaceURI for Attr. 
> 
> ???  How is it incorrect?

namespaceURI is defined for Node, not Attr - it is only inherited from
Node into Attr. No other inherited attributes are ever mentioned in
the specialized interfaces.

> It would be nice in these descriptions to give short explanations of
> special values, such as what a namespaceURI of "" or None means.

Indeed. In particular, it is important to explain whether an "absent"
DOMString attribute is represented by an empty string, or by None.

Regards,
Martin