有谁知道为什么这个编译成功？

int main()
{
   // forward declaration
   struct myStruct_st *mS; // Note that this will expand as "struct struct myStruct_st *mS which does not make any sense to me"

   return 0;
}

// definition of myStruct_s
typedef struct myStruct_s
{
   int x;
   int y;
} myStruct_st;
int main()
{
   // forward declaration
   struc