What is the difference between 'protected' and 'protected internal'?

Question

Can someone please explain the difference between the protected and protected internal modifiers in C#? It looks like their behavior is identical.

Answer 1

The "protected internal" access modifier is a union of both the "protected" and "internal" modifiers.

From MSDN, Access Modifiers (C# Programming Guide):

protected:

The type or member can be accessed only by code in the same class or struct, or in a class that is derived from that class.

internal:

The type or member can be accessed by any code in the same assembly, but not from another assembly.

protected internal:

The type or member can be accessed by any code in the assembly in which it is declared, OR from within a derived class in another assembly. Access from another assembly must take place within a class declaration that derives from the class in which the protected internal element is declared, and it must take place through an instance of the derived class type.

Note that: protected internal means "protected OR internal" (any class in the same assembly, or any derived class - even if it is in a different assembly).

...and for completeness:

private:

The type or member can be accessed only by code in the same class or struct.

public:

The type or member can be accessed by any other code in the same assembly or another assembly that references it.

private protected:

Access is limited to the containing class or types derived from the containing class within the current assembly.
(Available since C# 7.2)