When examining the class definition of a derived class, documentation is needed to determine which members are virtual. Specifying 'virtual' explicitly helps to document the class.

   
   class A
   {
   public:
      virtual void f();
      virtual void operator+( A const& );
      virtual ~A();
   };
   
   class B1 : public A 
   {
   public:
      virtual void f();                      // virtual: make explicit
      virtual void operator+( A const& );    // virtual: make explicit
      virtual ~B1();                         // virtual: make explicit
   };