Add remark about timeout scope on HttpCompletionOptions enum

snippets/csharp/System.Net.Http/HttpCompletionOption/HttpCompletionOptionSnippets.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Net.Http;
+using System.Threading.Tasks;
+
+namespace HttpCompletionOptionSnippets
+{
+    class HttpCompletionOptionSnippets
+    {
+        public static async Task RunAsync()
+        {
+            //<SnippetHttpCompletionOption>
+            var httpClient = new HttpClient();
+            httpClient.Timeout = TimeSpan.FromSeconds(30);
+            using (var response = await httpClient.GetAsync("http://localhost:12345/", HttpCompletionOption.ResponseHeadersRead)) // 30-second timeout but ONLY up until past the headers
+            {
+                // Do other stuff that doesn't rely on the content first, like status code validation
+                response.EnsureSuccessStatusCode();
+
+                var content = await response.Content.ReadAsStringAsync(); // NO TIMEOUT
+            }
+            //</SnippetHttpCompletionOption>
+        }
+    }
+}

snippets/csharp/System.Net.Http/HttpCompletionOption/HttpCompletionOptionSnippets.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

snippets/csharp/System.Net.Http/HttpCompletionOption/Program.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace HttpCompletionOptionSnippets
+{
+    class MetadataReaderSnippets
+    {
+        class Program
+        {
+            static async Task Main()
+            {
+                await HttpCompletionOptionSnippets.RunAsync();
+            }
+        }
+    }
+}

xml/System.Net.Http/HttpCompletionOption.xml

@@ -36,7 +36,17 @@
   </Base>
   <Docs>
     <summary>Indicates if <see cref="T:System.Net.Http.HttpClient" /> operations should be considered completed either as soon as a response is available, or after reading the entire response message including the content.</summary>
-    <remarks>To be added.</remarks>
+    <remarks>
+      <format type="text/markdown"><![CDATA[
+
+## Remarks
+ The <xref:System.Net.Http.HttpCompletionOption> value effectively affects the scope of the timeout specified in the <xref:System.Net.Http.HttpClient> operation options when reading a response. The timeout on the <xref:System.Net.Http.HttpClient> always applies on the relevant invoked methods up until the point where those methods complete/return. Crucially, when using the <xref:System.Net.Http.HttpCompletionOption.ResponseHeadersRead> option, the timeout applies only up to where the headers end and the content starts. The content reading operation needs to be timed out separately in case the server promptly returns the status line and headers but takes too long to return the content. Below is an example illustrating this point:
+
+ :::code language="csharp" source="~/snippets/csharp/System.Net.Http/HttpCompletionOption/HttpCompletionOptionSnippets.cs" id="SnippetHttpCompletionOption":::
+
+ ]]>
+      </format>
+    </remarks>
   </Docs>
   <Members>
     <Member MemberName="ResponseContentRead">