What does <?..?> mean in XML?

Question

What does <?..?> mean in XML?

Example:

<?xml version="1.0" encoding="UTF-8"?>
<tests>
<test><?xml-multiple ?>
</test>
</tests>

I want to know what <?xml-multiple ?> means in the above XML? I syntax-checked this XML in w3schools, there is no error.

Answer 1

This is a processing instruction. Processing instructions are used to directly pass on some information or instruction to the application via the parser, but without the parser actually interpreting it.

<?my-application some instructions ?>

The token after the initial question mark (here my-application) is called the target and identifies the application at which the instruction is aimed. What follows it is not further specified by XML, is treated by the parser as a black box, and it is up to the application to interpret it. Entity and character references are not recognized.

Processing instructions with the target xml-multiple seem to be commonly produced, accepted and recognized by applications that transform XML to JSON or JSON to XML (including Oracle) in order to identify arrays, even though I am not sure where and if its behavior is officially standardized.

Processing instructions are not to be confused with the initial <?xml version="1.0"?>, which is called a text declaration.