Why not PIs for namespace declarations?

Clark C. Evans clark.evans at manhattanproject.com
Thu Dec 23 20:01:08 GMT 1999

On Thu, 23 Dec 1999, Andrew Layman wrote:
> Clark Evans asks why PIs are not the mechanism for namespace declaration.
> That option was extensively debated during the design process (see the
> archives for details).  The short answer is that PIs do not have tree scope,
> so are unsuitable for modular document construction.

This specific problem points out to a flaw in the PI 
mechanism that could have been fixed... rather than 
creating a "work-around" -- as David pointed out, not
many tools were compliant anyway!  For example, this 
could have been easily fixed by altering the XML syntax 
to allow for PI's to occur within elements...

    <!-- pi's scope ends here -->

I'm sure the "backward compatible" drum was used,
however, in the XML world, unlike the bulk of
programming tradition, the data outlives the
program, not the other way around.   Thus, this
would have been backward-data compatible, which
is the only concern.  Specific versions of programs
typically have a shelf life for less than 2-3 years,
where data can last for decades.  On the other hand, 
how is having xmlns:prefix="uri" going to mess up
programs that expect processing instructions to
appear in PIs -- ones that show attributes directly
to end-users.

So, is a long-term fix in the works?  Or are we going 
to keep using attributes for processing instructions
and deprechate the unapprechiated PI mechanism?



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