Clarify the status of dyn_array

CppCoreGuidelines.md

@@ -21341,7 +21341,7 @@ Use `not_null<zstring>` for C-style strings that cannot be `nullptr`. ??? Do we
 * `unique_ptr<T>`     // unique ownership: `std::unique_ptr<T>`
 * `shared_ptr<T>`     // shared ownership: `std::shared_ptr<T>` (a counted pointer)
 * `stack_array<T>`    // A stack-allocated array. The number of elements is determined at construction and fixed thereafter. The elements are mutable unless `T` is a `const` type.
-* `dyn_array<T>`      // ??? needed ??? A heap-allocated array. The number of elements is determined at construction and fixed thereafter.
+* `dyn_array<T>`      // A container, nongrowing dynamically allocated array. The number of elements is determined at construction and fixed thereafter.
   The elements are mutable unless `T` is a `const` type. Basically a `span` that allocates and owns its elements.
 
 ## <a name="SS-assertions"></a>GSL.assert: Assertions
@@ -22177,7 +22177,8 @@ No. `stack_array` is guaranteed to be allocated on the stack. Although a `std::a
 
 ### <a name="Faq-gsl-dyn-array"></a>FAQ.58: Is `dyn_array` the same as `vector` or the proposed `dynarray`?
 
-No. `dyn_array` is not resizable, and is a safe way to refer to a heap-allocated fixed-size array. Unlike `vector`, it is intended to replace array-`new[]`. Unlike the `dynarray` that has been proposed in the committee, this does not anticipate compiler/language magic to somehow allocate it on the stack when it is a member of an object that is allocated on the stack; it simply refers to a "dynamic" or heap-based array.
+No. `dyn_array` is a container, like `vector`, but it is not resizable; its size is fixed at runtime when it is constructed.
+It is a safe way to refer to a dyamically "heap"-allocated fixed-size array. Unlike `vector`, it is intended to replace array-`new[]`. Unlike the `dynarray` that has been proposed in the committee, this does not anticipate compiler/language magic to somehow allocate it on the stack when it is a member of an object that is allocated on the stack; it simply refers to a "dynamic" or heap-based array.
 
 ### <a name="Faq-gsl-expects"></a>FAQ.59: Is `Expects` the same as `assert`?