Document efficient multi-value string comparisons using SearchValues

docs/core/whats-new/dotnet-8/runtime.md

@@ -513,7 +513,8 @@ IDataView predictions = model.Transform(split.TestSet);
   }
   ```
 
-- Methods like <xref:System.MemoryExtensions.IndexOfAny%2A?displayProperty=nameWithType> look for the first occurrence of *any value in the passed collection*. The new <xref:System.Buffers.SearchValues%601?displayProperty=fullName> type is designed to be passed to such methods. Correspondingly, .NET 8 adds new overloads of methods like <xref:System.MemoryExtensions.IndexOfAny%2A?displayProperty=nameWithType> that accept an instance of the new type. When you create an instance of <xref:System.Buffers.SearchValues%601>, all the data that's necessary to optimize subsequent searches is derived *at that time*, meaning the work is done up front.
+- Methods like <xref:System.MemoryExtensions.IndexOfAny%2A?displayProperty=nameWithType> look for the first occurrence of *any value in the passed collection*. The new <xref:System.Buffers.SearchValues%601?displayProperty=fullName> type is designed to be passed to such methods. Correspondingly, .NET 8 adds new overloads of methods like <xref:System.MemoryExtensions.IndexOfAny%2A?displayProperty=nameWithType> that accept an instance of the new type. When you create an instance of <xref:System.Buffers.SearchValues%601>, all the data that's necessary to optimize subsequent searches is derived *at that time*, meaning the work is done up front. 
+For guidance on using `SearchValues<T>` for efficient multi-value string comparisons, see [Efficient multi-value string comparisons](../../standard/base-types/string-comparison.md#efficient-multi-value-string-comparisons).
 - The new <xref:System.Text.CompositeFormat?displayProperty=fullName> type is useful for optimizing format strings that aren't known at compile time (for example, if the format string is loaded from a resource file). A little extra time is spent up front to do work such as parsing the string, but it saves the work from being done on each use.
 
   ```csharp

docs/standard/base-types/string-comparison-net-5-plus.md

@@ -331,6 +331,38 @@ ReadOnlySpan<char> span = s.AsSpan();
 if (span.StartsWith("Hello", StringComparison.Ordinal)) { /* do something */ } // ordinal comparison
 ```
 
+## Efficient multi-value string comparisons
+
+When comparing a string against a fixed set of known values repeatedly, consider using `SearchValues<T>` instead of chained comparisons or LINQ-based approaches.
+`SearchValues<T>` can precompute internal lookup structures and optimize the comparison logic based on the provided values.
+
+### Recommended usage
+
+Create and cache the `SearchValues<string>` instance once, then reuse it for comparisons:
+
+```cs
+using System.Buffers;
+
+private static readonly SearchValues<string> Commands = SearchValues.Create(new[] { "start", "run", "go" }, StringComparison.OrdinalIgnoreCase);
+
+if (Commands.Contains(command))
+{
+    /* do something */
+}
+```
+### Avoid repeated creation
+Avoid creating `SearchValues` instances inside hot paths or per comparison, as the creation step can be relatively expensive:
+
+```cs
+// Avoid this pattern
+if (SearchValues.Create(new[] { "start", "run", "go" }, StringComparison.OrdinalIgnoreCase).Contains(command))
+{
+ /* do something */
+}
+```
+Caching and reusing the instance ensures optimal performance.
+
+
 ## See also
 
 - [Globalization breaking changes in .NET 5](../../core/compatibility/5.0.md#globalization)