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Re: PIs considered harmful Was: XML-SW, a thought experiment

From: Simon St.Laurent <simonstl@simonstl.com>
Date: 12 Feb 2002 18:06:18 -0500
To: "'www-tag'" <www-tag@w3.org>
Message-Id: <1013555179.1027.325.camel@localhost.localdomain>
On Tue, 2002-02-12 at 15:03, Tim Berners-Lee wrote:
> PIs are indeed "useful in practice".  However, I feel they are harmful
> because they bypasss all the extensibility power one has with namespaces
> to make well-defined extentsions.

That didn't need to have been the case.  Namespaces in XML didn't
specify processing for colons in PI targets, but it wouldn't have been
much more difficult (IMHO) to create a multi-part name for PIs than for
elements and attributes.  

> PIs also add a barnacle onto the XML syntax which it really doesn't need.

Not much of a barnacle, and one which definitely fits well with the
notion of "Extensible" Markup Language.

> The idea of namespaces is that you can use one to define a new
> element to do just what you wanted to do with the PI, but you give
> it a URI name, and allow possibilities such as using existing tools
> for parsing and test for and converting them and so on.
> What is there which stops you using an element?

Validation, in most of its forms.  If you'd be willing to throw
validation out, I think we'd have a lot less need for PIs.
> PIs are in concept a significant security liability, because different
> processors will
> process them differently, and so one will be able to make a document
> wheich will seem one thing in one case and another thing in another
> case, without the XML system being offically aware of it.

And different applications will process XML element and attribute
content differently, and may in fact suffer security issues when faced
with (perhaps valid but) unexpected structures.

> I would agree with David and hope that PIs would be eliminated as soon as
> possible.

I would hope that the W3C would drop its continuing institutional animus
against processing instructions.  If there is a need to blast some bit
of XML's SGML heritage as incompatible with the Web, may I suggest
notations, unparsed entities, or both.
Simon St.Laurent
Ring around the content, a pocket full of brackets
Errors, errors, all fall down!
Received on Tuesday, 12 February 2002 17:01:52 UTC

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