What might the 'friend' keyword inside a class definition do?

The 'friend' keyword in a class definition allows a function or another class to have special access to private members of the class. This means that the 'friend' class or function can access and modify private data members, which are not accessible to other classes or functions. Option A is incorrect because the 'friend' keyword does not declare another class, it only grants access to the private members of a particular class. Option B is incorrect because the 'friend' keyword does not limit the class's visibility, it grants access. Option D is incorrect because declaring a member function would not require the use of the 'friend' keyword.