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   Re: [xml-dev] Processing instruction guidelines

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I try to use processing instructions only for things that are really
specific to one and only one application and that are not intrinsic to
the document's content. I prefer to put anything that:
   - should be used by more than one application,
   - would be useful in the future (when other tools may be used), or
   - is a real part of the information, 
into the element/attribute structure of the document. 

I like to use processing instructions for information I want to "hide" 
from (some) XML applications, but that should be available other 

One use of PIs that we at Mulberry use a lot is in sample documents.
We want the samples of documents we provide with DTDs and Schemas to
be valid (of course).  But we also want to display parts of the
documents at appropriate places in the application documentation. 
We put processing instructions in the samples to specify which
portion(s) of each sample should be displayed in the documentation.
This leaves us with samples that are still valid according to the 
schema/DTD we are documenting, but we that we can manipulate as
needed. It's a major timesaver as the Schema/DTD changes and we want
to re-validate all of the samples.

I think it is generally bad practice to use PIs for things that many/any 
application(s) manipulating the content will need access to (for example, 
graphics placement instructions). It is good practice to use them for 
one-time use application-specific information (for example, in many 
situations, forced column-breaks and over-rides to hyphenation/justification

-- Tommie

B. Tommie Usdin                        mailto:btusdin@mulberrytech.com
Mulberry Technologies, Inc.                http://www.mulberrytech.com    
17 West Jefferson Street                           Phone: 301/315-9631 
Suite 207                                    Direct Line: 301/315-9634 
Rockville, MD  20850                                 Fax: 301/315-8285 
  Mulberry Technologies: A Consultancy Specializing in SGML and XML               


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