From Namespaces in XML 1.1 ( 2004-02-04) A namespace (or more precisely, a namespace binding) is declared using a family of reserved attributes. Such an attribute's name must either be xmlns or begin xmlns:. These attributes, like any other XML attributes, may be provided directly or by default.
From Namespaces in XML ( 1999-01-14) A namespace is declared using a family of reserved attributes. Such an attribute's name must either be xmlns or have xmlns: as a prefix. These attributes, like any other XML attributes, may be provided directly or by default.