C# wird ja immer weiterentwickelt. Das geht seit Roslyn so schnell, dass manche Sachen dort vielleicht untergegangen sind. Z. B. hat C# mittlerweile zwei neue Access-Modifiers, die noch “so üblich” sind:

• protected internal: The type or member can be accessed by any code in the assembly in which it’s declared, or from within a derived class in another assembly.
• private protected: The type or member can be accessed only within its declaring assembly, by code in the same class or in a type that is derived from that class.