Clarify that rune isn't available in .NET Framework (#43164)

Author: adegeo

docs/standard/base-types/character-encoding-introduction.md

@@ -1,7 +1,7 @@
 ---
 title: Introduction to character encoding in .NET
 description: Learn about character encoding and decoding in .NET.
-ms.date: 08/11/2021
+ms.date: 10/22/2024
 ms.topic: conceptual
 no-loc: [Rune, char, string]
 dev_langs:
@@ -181,7 +181,10 @@ The following diagram illustrates the scalar value code points.
 
 ### The Rune type as a scalar value
 
-Beginning with .NET Core 3.0, the <xref:System.Text.Rune?displayProperty=fullName> type represents a Unicode scalar value. **`Rune` is not available in .NET Core 2.x or .NET Framework 4.x.**
+> [!IMPORTANT]
+> The `Rune` type isn't available in .NET Framework.
+
+In .NET, the <xref:System.Text.Rune?displayProperty=fullName> type represents a Unicode scalar value.
 
 The `Rune` constructors validate that the resulting instance is a valid Unicode scalar value, otherwise they throw an exception. The following example shows code that successfully instantiates `Rune` instances because the input represents valid scalar values:
 
@@ -265,8 +268,6 @@ In .NET APIs, a grapheme cluster is called a *text element*. The following metho
 
 :::code language="csharp" source="snippets/character-encoding-introduction/csharp/CountTextElements.cs" id="SnippetCallCountMethod":::
 
-If you run this code in .NET Framework or .NET Core 3.1 or earlier, the text element count for the emoji shows `4`. That is due to a bug in the `StringInfo` class that was fixed in .NET 5.
-
 ### Example: splitting string instances
 
 When splitting `string` instances, avoid splitting surrogate pairs and grapheme clusters. Consider the following example of incorrect code, which intends to insert line breaks every 10 characters in a string: