Processing instructions (was XSchema: Sections 5.0 and 5.1)

david at david at
Fri Sep 25 17:38:19 BST 1998

John Cowan writes:

 > PIs are extremely useful when adding information to documents with
 > frozen DTDs.  For example, the proposed "xml:stylesheet" PI allows you
 > to attach a stylesheet to any XML document without having to
 > tamper with the document's DTD (as by adding a STYLE element
 > or attribute).
 > I can't see designing a new document type and using PIs, though.
 > As you say, elements or attributes do the work.

PI's provide a (slightly clumsy) method for adding new declaration
types to XML without breaking existing parsers.  In general, I don't
think that it's a good idea to use elements and attributes for
declarations, since they represent the logical structure of the
document itself.

All the best,


David Megginson                 david at

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