xmlns:xi XInclude Namespace Declaration
This is not an attribute, but the namespace pseudo-attribute. The value provides a namespace prefix and URI to use for the XInclude elements. All namespace prefixes must be associated with a URL, and the prefix “xi” has been set to the URL for the World Wide Web Consortium (W3C) XInclude Recommendation.
FIXED (not settable) on many elements; click for list and usage
|http://www.w3.org/2001/XInclude||The prefix “xi” has been set to the URL for the W3C XInclude Recommendation.|
|Restriction||This attribute has a fixed value which may not be changed in the XML document.|