Each XML documents SHOULD begin with an XML declaration which specifies the version of XML being used.
<?xml version="1.0"?>
<greeting>Hello, world!</greeting>
The version of XML being used.
<?xml version="1.0"?>
In a standalone document declaration, the value “yes” indicates that there are no external markup declarations which affect the information passed from the XML processor to the application.
<?xml version="1.0" standalone='yes'?>