The prolog of an XML document, when present, precedes the document element.
The prolog may, but need not, contain the following:
An XML declaration
Miscellaneous content—processing instructions or comments
A Document Type Declaration, also called a DOCTYPE declaration
Let’s look at each of these in turn.
The XML declaration can be as simple as this:
<?xml version="1.0" ?>
This declaration is an optional part of all XML documents. However, when an XML declaration is present in an XML document, it must occur in the first line of the XML document and must have no characters—not even a single space character—before it.
An XML declaration, if present, must have a version attribute. For XML documents that correspond to ...