Processing instructions are used to embed information intended for proprietary applications. The XML declaration is an example of a processing instruction. Processing instructions beginning with 'xml' or 'XML' have been reserved for standardization in the XML Version 1.0 specification and onwards.
- PI_target: any name that does not contain the letters 'X' or 'x', 'M' or 'm', or 'L' or 'l' in that order.
<?word document="test.doc" ?>
- The string '?>' cannot be placed within a processing instruction, therefore, nested processing instructions are not allowed.