XML Base recommendation was adopted on 2001-06-27.
The attribute xml:base may be inserted in XML documents to specify a base URI other than the base URI of the document or external entity. The value of this attribute is interpreted as a URI Reference as defined in RFC 2396 [IETF RFC 2396], after processing according to Section 3.1.
In namespace-aware XML processors, the "xml" prefix is bound to the namespace name http://www.w3.org/XML/1998/namespace as described in Namespaces in XML [XML Names]. Note that xml:base can be still used by non-namespace-aware processors.