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   [xml-dev] RE: On Schemas, Namespaces and Syntax vs. Semantics(long but w

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At 2:53 AM -0700 7/28/02, Dare Obasanjo wrote:

>a.) The only difference between using attributes from a special 
>processing namespace and PIs is that the attributes can be validated 
>while the PIs cannot. Everything else you mentioned is a red herring.

I disagree on two points:

1. PIs can be validated provided you use a language that supports 
this, such as Schematron.

2. PIs don't are not validated by default in any schema language I 
know of. Thus they can slip in behind the back of schemas and 
validation software in a way that attributes can't. This is exactly 
the behavior that's needed to avoid "severely crufty 
executable-comment embedded languages".

Processing instructions are a positive *good*. They make it possible 
to provide useful information intended for specific, named processes 
which does not apply to all processes processing a document. This is 
especially true when the targetted process should operate on 
documents from multiple XML applications. The classic examples are 
Web browsers with xml-stylesheet processing instructions and the 
Cocoon application server with cocoon processing instructions.

| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
|          XML in a  Nutshell, 2nd Edition (O'Reilly, 2002)          |
|              http://www.cafeconleche.org/books/xian2/              |
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