Why not PIs for namespace declarations?

David Brownell david-b at pacbell.net
Thu Dec 23 21:17:17 GMT 1999

"Clark C. Evans" wrote:
> 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.

Bad short answer; see below.

More accurate is that certain person (or persons) disliked
PIs extremely, if even a tenth of what I've heard is accurate.
The debate on this was comparable to the recent "how many XHTMLs
are there" namespace debate.

> 	 For example, this
> could have been easily fixed by altering the XML syntax
> to allow for PI's to occur within elements...

But XML _does_ permit this.  Check the grammar, or almost
any XML processor ... this was an easy bit to get right!

What you're suggesting is that PIs be lexically scoped.
(That's what Andrew seems to mean by "tree" scope.)

And in fact, there's nothing in the world preventing the
definition of a particular PI from using lexical scope.
One doesn't need all PIs to work that way; only one.

> <parent>
>   <child>
>     <?pi?>
>     <grandchild/>
>     <!-- pi's scope ends here -->
>   </child>
> </parent>

I've no intention of reopening the debate on this topic
(we're stuck with attributes), but I've got this strange
belief that truth should be told, so I couldn't let this
one slip by.

- Dave

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