To use Identifier1, there needs to be a definition for Identifier2, which is a type. 

Example where __classid is the first identifier and TClass, which can be found in clx.h, is the second one:

// #include <clx/clx.h> missing
struct __declspec(delphiclass)bar
{
     virtual int barbara(void);
};
void *foo(void)
{
     return classid(bar);    // Error
}