Re: do you use pi's?

Subject: Re: do you use pi's?
From: "Liam R. E. Quin" <liamquin@xxxxxxxxxxxx>
Date: Sun, 4 Apr 1999 03:19:07 -0400 (EDT)
Mark D. Anderson <mda@xxxxxxxxxxxxxx> wrote:
> Comments? Does XML need PI's?

At one time there was a widespread idea that a processing instruction
should not alter the "semantics" (in some unspecified way) of an
SGML document.

In practice, this meant that it was often considered acceptable to
strip out all comments and processing instructions from SGML documents
before processing it, or, to ignore processing instructions except
those directed towards a specific application.

XML has begun to blur the distinction between processing instructions
and markup declarations.

The XML Declaration <?xml version="1.0"?> looks so much like a
processing instruction that I have seen an XML book refer to it as
one.  The style sheet PI has been added, and no doubt we'll see more
in the future.  This is because SGML did not allow a way of defining
one's own markup declarations, and also did not allow markup declarations
in the body of the document.

It is no longer a simple matter of being able to ignore all processing
instructions.

There was never any formal need for processing instructions.
They were simply convenient.

But now we have them, and are stuck with them.  I'm not sure it's
such a bad thing really.  Given a choice between eliminating CDATA
sections, comments, processing instructions, multi-valued tokenised
attributes and some other feature, I admit I'd be interested in getting
rid of PIs.

I might have argued for:
<XML>
  <stylehsheet href="xxx" type="yyy">
    <menu>Big Type</menu>
    <desc>Large type and clear colours for easier readability</desc>
  </stylesheet>
</XML>

When XML was being developed, this was argued against because it
"polluted the element name space" by using the name "XML" -- which was
later reserved anyway.  With namespaces in place, an XML element looks
a lot more desirable to me.

But history cannot be changed, and when you have built a cathedral,
you had better hold services in it instead of wishing you had built
a stock exchange instead.

Lee

-- 
Liam Quin, GroveWare Inc., Toronto;  The barefoot agitator
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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