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Re: [xml-dev] RE: Formatting Processing Instructions

From: Michael Kay <mike@--------.--->
To: xml-dev@-----.---.---
Date: 2/23/2012 9:33:00 AM
On 22/02/2012 20:30, David Lee wrote:
>
> I for one have NEVER used a PI nor have ever encountered one nor have 
> ever found any desirable use for one.
>
>
I admit to occasional use of PIs. Here are some of the ways I have used 
them:

- metadata in XSLT test stylesheets, where I want confidence that the 
metadata will be thrown away by the XSLT processor. I could use a 
top-level data element, but that would involve declaring a namespace, 
and the extra namespace could in theory disturb the test.

- an alternative to entity references or numeric character references 
that will survive XSLT transformation without making the document 
DTD-invalid or schema-invalid. Doesn't work in attributes, of course.

- an instruction to the XSLT processor, like <?generate-glossary-here?>. 
Shouldn't this be an element? Perhaps yes; I'm doing this where I 
control the XSLT processing but not the schema/DTD, so it's a form of 
tag abuse. But it would probably be wrong to add the element to the 
schema/dtd, because there are really two content models here: the "raw" 
content and the "preprocessed" content, and the PI appears only in the 
raw content, while the schema describes the structure of the 
preprocessed content. I'm using a PI so that I can use one DTD/schema 
for both content models.

And I would defend it as better than using dummy content like

<div id="glossary">
<head>#insert-glossary-here#</head>
</div>

which I have also been known to do.

Michael Kay
Saxonica

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