[basic.pre] unintended re-definition of `declaration`

It seems to me that 6.1.5 is formulated in a way that suggest that the sentence is actually a definition of declaration - and it is not:

Every name is introduced by a declaration, which is a [...]

According my interpretation of this Grammarly blog post, the ", which is a [...]" part is a nonrestrictive clause. That means that the sentence should make sense even without it, and the clause should only add some additional information. So the sentence is equivalent to saying

Every name is introduced by a declaration. By the way, a declaration is a [...]

But then (1) we would have two definitions of what a declaration is, and (2) we would not restrict which kinds of declarations can introduce names. This would be in contrast with what I am guessing is the intended meaning of the sentence - that is, to define the "can-introduce-a-name" property of declaration. In my opinion, the sentence should go like this:

Every name is introduced by a declaration that is a [...]

(that is, we should use a restrictive clause).

Disclaimer: I am not a native English speaker.

Start by reading the wording in C++ draft section 6.1.5 and the linked definition of declaration. Check whether the sentence's relative clause is restrictive and whether it limits which declarations introduce names. Done means the wording expresses the intended restriction without suggesting a second definition.