Processing Instruction

Source: Wikipedia, the free encyclopedia.

A processing instruction (PI) is an

SGML and XML node type, which may occur anywhere in a document, intended to carry instructions to the application.[1][2]

Processing instructions are exposed in the Document Object Model as Node.PROCESSING_INSTRUCTION_NODE, and they can be used in XPath and XQuery with the 'processing-instruction()' command.

Syntax

An SGML processing instruction is enclosed within <? and >.[3]

An XML processing instruction is enclosed within <? and ?>, and contains a target and optionally some content, which is the node value, that cannot contain the sequence ?>.[4] 

<?PITarget PIContent?>

The XML Declaration at the beginning of an XML document (shown below) is another example of a processing instruction,[5] however it may not technically be considered one.[6] 

<?xml version="1.0" encoding="UTF-8" ?>

Examples

The most common use of a processing instruction is to request the XML document be rendered using a

CSS
stylesheets. 

<?xml-stylesheet type="text/xsl" href="style.xsl"?>

<?xml-stylesheet type="text/css" href="style.css"?>

The DocBook XSLT stylesheets understand a number of processing instructions to override the default behaviour.[8]

A draft specification for

Robots exclusion standard rules inside XML documents uses processing instructions.[9]

References

  1. ISBN 978-0974152134
    .
  2. ^ Comparison of SGML and XML; World Wide Web Consortium Note, 15 December 1997
  3. ISBN 0-201-40394-3
    . Retrieved 2010-08-18.
  4. ISBN 0-471-22203-8
    .
  5. ^ "XML 1.0 - slide "Processing Instructions (PIs)"". www.w3.org. Retrieved 2023-02-08.
  6. ISBN 978-0-596-00764-5
    .
  7. ^ "Associating Style Sheets with XML documents 1.0 (Second Edition)".
  8. ^ "Part 2. FO Processing Instruction Reference".
  9. ^ "Robots Processing Instruction Homepage". Archived from the original on 2010-09-21. Retrieved 2010-08-18.

External links

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