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 3986 . It serves the function described in section 5.1.1 of RFC3986, establishing the base URI (or IRI) for resolving any relative references found within the effective scope of the xml:base attribute.
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 . Note that xml:base can be still used by non-namespace-aware processors.