xml declaration
A valid Open eBook is a valid XML document and therefore must contain an XML declaration. This tag identifies a document as an xml document and must precede all other tags and content. Note that there is no corresponding end-marker. This tag is often added by content formatting tools and may not be of significance to most content developers.

attributes

version
specifies the XML version number.
encoding
specifies the XML encoding character set. UTF-8 is recommended.