c++ - What do they mean by the sentence "is used to identify the subject of an elaborated-type-specifier" in [dcl.typedef]/8?

Question

[dcl.typedef]/8

A simple-template-id is only a typedef-name if its template-name names an alias template or a template template-parameter. [Note 1: A simple-template-id that names a class template specialization is a class-name ([class.name]). If a typedef-name is used to identify the subject of an elaborated-type-specifier ([dcl.type.elab]), a class definition, a constructor declaration, or a destructor declaration, the program is ill-formed. — end note]

[Example 8:

struct S {
    S();
    ~S();
};

typedef struct S T;

S a = T();                      // OK
struct T * p;                   // error

— end example]

I presume the sentence highlighted above explains the error. But I'm not sure I understand what do they mean by that sentence.

Answer 1

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