A namespace-alias-definition declares an alternate name for a namespace according to the following grammar:
namespace-alias: identifier
namespace-alias-definition: namespace identifier = qualified-namespace-specifier ;
qualified-namespace-specifier: nested-name-specifieropt namespace-name
The identifier in a namespace-alias-definition is a synonym for the name of the namespace denoted by the qualified-namespace-specifier and becomes a namespace-alias. [ Note: When looking up a namespace-name in a namespace-alias-definition, only namespace names are considered, see [basic.lookup.udir]. — end note ]
In a declarative region, a namespace-alias-definition can be used to redefine a namespace-alias declared in that declarative region to refer only to the namespace to which it already refers. [ Example: The following declarations are well-formed:
namespace Company_with_very_long_name { /* ... */ }
namespace CWVLN = Company_with_very_long_name;
namespace CWVLN = Company_with_very_long_name; // OK: duplicate
namespace CWVLN = CWVLN;— end example ]