Clarify index and range usages (#46496)

Fixes #44907 Indexes and ranges are only usable with single dimensional arrays, not multi-dimensional arrays.

Author: BillWagner

docs/csharp/language-reference/operators/member-access-operators.md

@@ -1,7 +1,7 @@
 ---
 title: "Member access and null-conditional operators and expressions:"
 description: "C# operators that you use to access type members or null-conditionally access type members. These operators include the dot operator - `.`, indexers - `[`, `]`, `^` and `..`, and invocation - `(`, `)`."
-ms.date: 04/04/2025
+ms.date: 05/29/2025
 author: pkulikov
 f1_keywords:
   - "._CSharpKeyword"
@@ -35,7 +35,7 @@ helpviewer_keywords:
 ---
 # Member access operators and expressions - the dot, indexer, and invocation operators.
 
-You use several operators and expressions to access a type member. Member access operators include member access (`.`), array element, or indexer access (`[]`), index-from-end (`^`), range (`..`), null-conditional operators (`?.` and `?[]`), and method invocation (`()`). These include the *null-conditional* member access (`?.`), and indexer access (`?[]`) operators.
+You use several operators and expressions to access a type member. Member access operators include member access (`.`), array element, or indexer access (`[]`), index-from-end (`^`), range (`..`), null-conditional operators (`?.` and `?[]`), and method invocation (`()`). These operators include the *null-conditional* member access (`?.`), and indexer access (`?[]`) operators.
 
 - [`.` (member access)](#member-access-expression-): to access a member of a namespace or a type
 - [`[]` (array element or indexer access)](#indexer-operator-): to access an array element or a type indexer
@@ -205,6 +205,9 @@ You also use parentheses to adjust the order in which to evaluate operations in
 
 Index and range operators can be used with a type that is *countable*. A *countable* type is a type that has an `int` property named either `Count` or `Length` with an accessible `get` accessor. [Collection expressions](./collection-expressions.md) also rely on *countable* types.
 
+> [!NOTE]
+> Single dimensional arrays are *countable*. Multi-dimensional arrays aren't. The `^` and `..` (range) operators can't be used in multi-dimensional arrays.
+
 The `^` operator indicates the element position from the end of a sequence. For a sequence of length `length`, `^n` points to the element with offset `length - n` from the start of a sequence. For example, `^1` points to the last element of a sequence and `^length` points to the first element of a sequence.
 
 :::code language="csharp" source="snippets/shared/MemberAccessOperators.cs" id="IndexFromEnd":::

docs/csharp/whats-new/csharp-13.md

@@ -1,7 +1,7 @@
 ---
 title: What's new in C# 13
 description: Get an overview of the new features in C# 13.
-ms.date: 01/27/2025
+ms.date: 05/29/2025
 ms.topic: whats-new
 ---
 # What's new in C# 13
@@ -71,7 +71,7 @@ You can read the details of the changes in the [proposal specification](~/_cshar
 
 ## Implicit index access
 
-The implicit "from the end" index operator, `^`, is now allowed in an object initializer expression. For example, you can now initialize an array in an object initializer as shown in the following code:
+The implicit "from the end" index operator, `^`, is now allowed in an object initializer expression for single-dimension collections. For example, you can now initialize a single-dimension array using an object initializer as shown in the following code:
 
 ```csharp
 public class TimerRemaining
@@ -103,7 +103,7 @@ In versions before C# 13, the `^` operator can't be used in an object initialize
 
 ## `ref` and `unsafe` in iterators and `async` methods
 
-This feature and the following two features enable `ref struct` types to use new constructs. You won't use these unless you write your own `ref struct` types. More likely, you'll see an indirect benefit as <xref:System.Span`1?displayProperty=nameWithType> and <xref:System.ReadOnlySpan`1?displayProperty=nameWithType> gain more functionality.
+This feature and the following two features enable `ref struct` types to use new constructs. You won't use these features unless you write your own `ref struct` types. More likely, you'll see an indirect benefit as <xref:System.Span`1?displayProperty=nameWithType> and <xref:System.ReadOnlySpan`1?displayProperty=nameWithType> gain more functionality.
 
 Before C# 13, iterator methods (methods that use `yield return`) and `async` methods couldn't declare local `ref` variables, nor could they have an `unsafe` context.