What is W3C's official position on use of PI?

Liam R. E. Quin liamquin at interlog.com
Fri May 14 03:03:32 BST 1999

On Wed, 12 May 1999, Paul Prescod wrote:

Paul Prescod <paul at prescod.net> wrote:
> Don Park wrote:
> > Thanks for clearing that up.  Do you what the folks who "regard PIs as
> > problematic second-class syntax" recommend for first-class out-of-band
> > signaling mechanism?  I wouldn't mind giving up PI if there was an
> > alternative.
> Well, Liam Quin has been a constant critic of processing instructions.

Heh... I always wanted to be remembered for something :-)

> http://www.mulberrytech.com/xsl/xsl-list/archive/msg03388.html
> http://www.lists.ic.ac.uk/hypermail/xml-dev/9811/0203.html

Well, if you read these -- especially the second -- you'll see that
they are not arguments against processing instructions.  The 2nd
article argues against using a processing instruction to link a
document to its style sheet in a way that was incompatible with
the then current XLink draft, and also incompatible with the DOM.

> [Paul's] response:
> http://www.mulberrytech.com/xsl/xsl-list/archive/msg03396.html
> As I said in that message, the important thing about processing
> instructions is that they are invisible to content models.

Yes.  This can be good and bad.  There's been a tendency in the SGML
world to use them like significant comments -- if you've ever seen a
large document with <?Pub Stuff> scattered all over it, you'll know
what I mean.  The usual reaction is that people in such environments
write scripts to remove all the processing instructions.

> If XML Schemas
> invented a way to make elements invisible to content models (like SGML's
> inclusion exceptions, but maybe only allowed at the top level) and a way
> to add these inclusions to existing schemas easily then processing
> instructions could be replaced by these "floating", element types. That
> would be neat.

I agree, and in some ways this could be where namespaces go, I think.

> But if there are no floating element types then we still need processing
> instructions.

Well, you don't need them in a formal sense, but I agree there there is
very strong motivation for them :-)


Liam Quin, independent SGML/XML/Unix/perl consultant
l i a m q u i n     at    i n t e r l o g    dot   c o m

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