eXtensible Markup Language (XML), is a plain text format used to store structured data. XML is written to be both human and machine readable.

XML documents often begin with a declaration, as shown here:

<?xml version="1.0"?> 

The declaration has three possible attributes. The version attribute is mandatory when a declaration is included:

• version: The XML version, 1.0 or 1.1
• encoding: The file encoding, most frequently utf-8 or utf-16
• standalone: Whether or not the XML file uses an internal or external Document Type Definition (DTD), permissible values are yes or no