RE: [xml-dev] Re: determining ID-ness in XML

["Champion, Mike" <Mike.Champion@SoftwareAG-USA.com>]

> -----Original Message-----
> From: Elliotte Rusty Harold [mailto:elharo@metalab.unc.edu]
> Sent: Wednesday, October 31, 2001 7:47 AM
> To: xml-dev@lists.xml.org
> Subject: RE: [xml-dev] Re: determining ID-ness in XML
> 
> "is xml+id"  non-uniqueness a well-formedness error, or will it 
> be some sort of
> >low-level validation error? Presumably a well-formedness error, since
> >non-validating parsers have no notion of "validation". 
> 
> This is the one tricky part. It is neither a well-formedness 
> error nor a validity error. It is violation of the xml:id 
> specification, but is in no way a violation of XML 1.0, 
> Namespaces in XML, or Schemas. Parsers would not, at least by 
> default, report such a violation unless a DTD or schema 
> declared that xml:id had type ID, in which case it becomes a 
> normal XML 1.0 or schemas validity error. 
> 
> It would be an error equivalent to xml:base="^^^^" or 
> anything else that is not a legal URI. That is, it is not an 
> XML 1.0 error. The XML parser will generally not flag this. A 
> client application that was aware of the extra semantics 
> attached to xml:id would catch the problem, much like an 
> XLink processor would catch a problem with the above xml:base 
> attribute but a normal XML parser would not. 

Ahhh, that makes sense to me!  And alleviates some of my other concerns; I
can see how it could be layered on top of XML and underneath Schema in the
short run, without causing too much pain in the interim while (presumably)
the various parsers and validators are moving to implement xml+id.