A '''Processingprocessing Instructioninstruction''' ('''PI''') is an [[SGML]] and [[XML]] node type, which may occur anywhere in thea document, intended to carry instructions to the application.<ref>{{Cite book |last=Stayton |first=Bob |title=DocBook XSL: The Complete Guide |chapter-url=http://www.sagehill.net/docbookxsl/ProcessingInstructions.html |publisher=Sagehill Enterprises |date=September 2007 |chapter=Chapter 9. Customization methods §Processing instructions |isbn=978-0974152134}}</ref><ref>[http://www.w3.org/TR/NOTE-sgml-xml-971215 Comparison of SGML and XML; World Wide Web Consortium Note, 15 December 1997]</ref>
Processing instructions are exposed in the [[Document Object Model]] as <code>Node.PROCESSING_INSTRUCTION_NODE</code>, and they can be used in [[XPath]] and [[XQuery]] with the 'processing-instruction()' command.
