feat(http): Add Prefer, Preferrence-Applied headers

files/en-us/web/http/headers/index.md

@@ -167,6 +167,13 @@ For more information, refer to the [CORS documentation](/en-US/docs/Web/HTTP/COR
 - {{HTTPHeader("Content-Location")}}
   - : Indicates an alternate location for the returned data.
 
+## Preference
+
+- {{HTTPHeader("Prefer")}}
+  - : Indicates preferences for specific server behaviors during request processing. For example, it can request minimal response content (`return=minimal`) or asynchronous processing (`respond-async`). The server processes the request normally if the header is unsupported.
+- {{HTTPHeader("Preference-Applied")}}
+  - : Informs the client which preferences specified in the `Prefer` header were applied by the server. It is a response-only header providing transparency about preference handling.
+
 ## Proxies
 
 - {{HTTPHeader("Forwarded")}}

files/en-us/web/http/headers/prefer/index.md

@@ -0,0 +1,74 @@
+---
+title: Prefer
+slug: Web/HTTP/Headers/Prefer
+page-type: http-header
+spec-urls: https://www.rfc-editor.org/rfc/rfc7240#section-2
+---
+
+{{HTTPSidebar}}
+
+The HTTP **`Prefer`** header allows clients to indicate preferences for specific server behaviors during request processing.
+
+> [!NOTE]
+> The `Prefer` header is often used in custom client-server implementations. Ensure both client and server support this header before relying on it in production.
+> The `Prefer` header does not cause the server to return an error if it does not support or apply the specified preferences. Instead, the server processes the request as if the header was not present.
+
+<table class="properties">
+  <tbody>
+    <tr>
+      <th scope="row">Header type</th>
+      <td>
+        {{Glossary("Request header")}}
+      </td>
+    </tr>
+    <tr>
+      <th scope="row">{{Glossary("Forbidden header name")}}</th>
+      <td>No</td>
+    </tr>
+  </tbody>
+</table>
+
+## Syntax
+
+```http
+Prefer: <preference>
+```
+
+## Directives
+
+- `respond-async`
+  - : Indicates that the client prefers asynchronous processing.
+- `return=minimal`
+  - : Requests that the server return minimal content.
+- `return=representation`
+  - : Requests a full resource representation in the response.
+- `wait=<seconds>`
+  - : Suggests how long the server should wait for the request to complete before timing out.
+- Custom preferences
+  - : Vendors or applications may define their own preferences to suit specific needs. For example, `custom-feature-enabled=true`.
+
+## Examples
+
+### Requesting minimal response
+
+```http
+GET /resource HTTP/1.1
+Host: example.com
+Prefer: return=minimal
+```
+
+### Requesting asynchronous processing
+
+```http
+POST /process HTTP/1.1
+Host: example.com
+Prefer: respond-async
+```
+
+## Specifications
+
+{{Specifications}}
+
+## See also
+
+- {{HTTPHeader("Preference-Applied")}}

files/en-us/web/http/headers/preference-applied/index.md

@@ -0,0 +1,61 @@
+---
+title: Preference-Applied
+slug: Web/HTTP/Headers/Preference-Applied
+page-type: http-header
+spec-urls: https://www.rfc-editor.org/rfc/rfc7240#section-3
+---
+
+{{HTTPSidebar}}
+
+The HTTP **`Preference-Applied`** header informs the client about which preferences from the `Prefer` request header were applied by the server.
+
+<table class="properties">
+  <tbody>
+    <tr>
+      <th scope="row">Header type</th>
+      <td>
+        {{Glossary("Response header")}}
+      </td>
+    </tr>
+    <tr>
+      <th scope="row">{{Glossary("Forbidden header name")}}</th>
+      <td>No</td>
+    </tr>
+    <tr>
+      <th scope="row">
+        {{Glossary("CORS-safelisted response header")}}
+      </th>
+      <td>No</td>
+    </tr>
+  </tbody>
+</table>
+
+## Syntax
+
+```http
+Preference-Applied: <preference>
+```
+
+## Examples
+
+### Server acknowledges a minimal response preference
+
+```http
+HTTP/1.1 200 OK
+Preference-Applied: return=minimal
+```
+
+### Server acknowledges an asynchronous processing preference
+
+```http
+HTTP/1.1 202 Accepted
+Preference-Applied: respond-async
+```
+
+## Specifications
+
+{{Specifications}}
+
+## See also
+
+- {{HTTPHeader("Prefer")}}