In p. 5 of the section 6.2 Declarations and definitions of the C++23 Standard there is written

5 In the definition of an object, the type of that object shall not be an incomplete type (6.8), an abstract class type (11.7.4), or a (possibly multi-dimensional) array thereof

Also in p.5 of the sub-section 6.8.1 General of the section 6.8 Types there is written

...The type of a pointer to array of unknown bound, or of a type defined by a typedef declaration to be an array of unknown bound, cannot be completed.

And further there is followed an example (Example 3)

class X; // X is an incomplete type

extern X* xp; // xp is a pointer to an incomplete type

extern int arr[]; // the type of arr is incomplete

typedef int UNKA[]; // UNKA is an incomplete type

UNKA* arrp; // arrp is a pointer to an incomplete type

UNKA** arrpp;

But according to the first provided quote this object definition

UNKA* arrp; // arrp is a pointer to an incomplete type

is invalid because such a pointer has an incomplete type.

So it looks like the example does not make sense or do I have missed something?

With best regards

(Vlad from Moscow)