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- From: email@example.com
- To: firstname.lastname@example.org
- Date: Wed, 02 Aug 2000 07:53:27 -0400
Paul W. Abrahams writes -
> I see PIs as something you wish to pass on to a particular processor or
> of processors. My sense of the matter (admittedly, unsupported by any
> documents I know of) is that they are, or ought to be, inessential to the
> general interpretation of a document. In other words, a well-formed and
> valid document ought to remain well-formed and valid if all PIs are
> Examples of PIs would be an indication that the following space character
> should be non-breaking or that a page break would be desirable at this
> point. These would be "tweaks" in the form of typographical hints, quite
> possibly particular to a specific version of a document typeset with one
> specific typesetting program, e.g., TeX.
With these kinds of usages in mind, you could consider PIs to be a different
kind of markup superimposed on a marked-up text. For example, an XML
document that contained RTF would have two more-or-less orthogonal markup
systems imposed on the underlying text. PIs are orthogonal to the rest of
the XML markup. So in a way, PIs represent a little bit of some undefined
orthogonal markup system. The XML provides the structural markup.
Furthermore, the PIs do not produce a self-delineating structure, which
again is quite different from (the rest of) XML.
Mabe this is the basic reason why so many people are uncomfortable with
PIs -they appear be be from a different, undefined system.