processing instructions def.

David Megginson david at
Wed Nov 24 16:28:09 GMT 1999

Benoit PAPILLAULT <Benoit.PAPILLAULT at> writes:

> I can't find a precise documentation on Processing Instruction, except
> on the W3C web server, but it's really not enough. Is there a more
> complete definition, along with real samples. I'm trying to implement
> some scripting features and 'm very interested in using XML Processing
> Instructions.

They're a black box.  In SGML, a processing instruction is just a
bunch of text, with no predefined meaning; in XML, the processing
instruction is a name followed optionally by a bunch of text, also
with no predefined meaning.  That means that an application should
look at a processing instruction and (usually) ignore it if it doesn't 
seem to make sense.

Of course, this isn't very robust, and there have been two suggestions 
for improvements:

1. The old XML WG considered allowing PI targets to be
   Namespace-qualified, but in the end there wasn't enough demand, and 
   the shift to attribute-based NS declarations would have killed that 

2. Various people have suggested following a lead from recent SGML
   developments and requiring the PI target to be a notation name.
   Since notations are almost never used in the XML world, that might
   be a non-starter.

All the best,


David Megginson                 david at

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