The XML Declaration must be at the exact start of the document (i.e. no whitespace leading the declaration).

It consists of three parts specified by pseudo-attributes:

1. version='n.n' -- specifies version information -- either 1.0 or 1.1.

2. encoding='type' -- specifies the unicode encoding used by this "data stream" to encode the unicode characters of the XML document.

3. standalone='yes|no' -- a specification of whether the document is sufficiently contained in the current character stream.

An example:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>