There is no way to restrict to a namespace. Namespaces are never units of protection. But if you're using assemblies, you can use the 'internal' access modifier to restrict access to only within the assembly.

Why do I get a syntax error when trying to declare a variable called checked?
The word checked is a keyword in C#.

Why are there five tracing levels in System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.