7 Declarations [dcl.dcl]

7.1 Specifiers [dcl.spec]

7.1.2 Function specifiers [dcl.fct.spec]

Function-specifiers can be used only in function declarations.

function-specifier:
    virtual
    explicit

The virtual specifier shall be used only in the initial declaration of a non-static class member function; see [class.virtual].

The explicit specifier shall be used only in the declaration of a constructor or conversion function within its class definition; see [class.conv.ctor] and [class.conv.fct].