[DOTNET-ROTOR] extern keyword

[Joe Mayo]

I was discussing the extern keyword on another list and someone showed
me this:

        /// <include file='doc\Assembly.uex'
path='docs/doc[@for="Assembly.CreateQualifiedName"]/*' />
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        public static extern String CreateQualifiedName(String
assemblyName, String typeName);

In this usage, what is the extern keyword doing?

Are there any other ways the extern keyword is used that isn't
documented?

Joe