2.2.1 [NamespacesXML1.1] Section 3, Declaring Namespaces

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C0001:

The specification states:

 Definition: 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.

IE9 Mode (All Versions)

Attributes that are used to declare a namespace binding must be provided directly.

C0002:

The specification states:

 The attribute's normalized value MUST be either a URI reference — the namespace 
 name identifying the namespace — or an empty string. The namespace name, to serve 
 its intended purpose, SHOULD have the characteristics of uniqueness and 
 persistence. It is not a goal that it be directly usable for retrieval of a 
 schema (if any exists). Uniform Resource Names [RFC2141] is an example of a 
 syntax that is designed with these goals in mind. However, it should be noted 
 that ordinary URLs can be managed in such a way as to achieve these same goals.

IE9 Mode (All Versions)

An empty string can be used as the value of the default namespace, but not any other specific namespace.