[Rules] Add response header accepts an expression (cloudflare#23786)

Author: pedrosousa

src/content/docs/rules/transform/response-header-modification/create-dashboard.mdx

@@ -31,10 +31,10 @@ To create a rule:
    :::
 
 8. For **Modify response header**, select one of the following operations:
-
+   - _Add static_ — Adds an HTTP response header with a static string value. This operation will not remove any existing response headers with the same name.
+   - _Add dynamic_ — Adds an HTTP response header according to the provided expression. This operation will not remove any existing response headers with the same name.
    - _Set static_ — Sets the value of an HTTP response header to a static string value. Overrides the value of any existing headers with the same name or adds a new header if it does not exist.
    - _Set dynamic_ — Sets the value of an HTTP response header according to the provided expression. Overrides the value of any existing headers with the same name or adds a new header if it does not exist.
-   - _Add_ — Adds an HTTP response header with a static string value. This operation will not remove any existing response headers with the same name.
    - _Remove_ — Removes the HTTP response header with the provided name, if it exists.
 
 9. Enter the name of the HTTP response header to modify in **Header name** and the static value or expression in **Value**, if you are setting the header value.

src/content/docs/rules/transform/response-header-modification/index.mdx

@@ -38,6 +38,7 @@ Through Response Header Transform Rules you can:
 - Set the value of an HTTP response header to a literal string value, overwriting its previous value or adding a new header to the response if it does not exist.
 - Set the value of an HTTP response header according to an expression, overwriting its previous value or adding a new header to the response if it does not exist.
 - Add a new HTTP response header with a literal string value without removing any existing headers with the same name.
+- Add a new HTTP response header according to an expression without removing any existing headers with the same name.
 - Remove an HTTP header from the response.
 
 You can create a response header transform rule [in the dashboard](/rules/transform/response-header-modification/create-dashboard/), [via API](/rules/transform/response-header-modification/create-api/), or [using Terraform](/terraform/additional-configurations/transform-rules/#create-a-response-header-transform-rule).
@@ -67,9 +68,7 @@ You can create a response header transform rule [in the dashboard](/rules/transf
 
 - Modifying `cache-control`, `CDN-Cache-Control`, or `Cloudflare-CDN-Cache-Control` headers will not change the way Cloudflare caches an object. Instead, you should create a [Cache Rule](/cache/how-to/cache-rules/).
 
-- To add a `set-cookie` header to the response, make sure you use the _Add_ operation instead of _Set static_/_Set dynamic_. Using one of the _Set_ operations will remove any `set-cookie` headers already in the response, including those added by other Cloudflare products such as Bot Management.
-
-- Currently you can only use the _Add_ operation with a literal string value.
+- To add a `set-cookie` header to the response, make sure you use one of the _Add static_/_Add dynamic_ operations instead of _Set static_/_Set dynamic_. Using one of the _Set_ operations will remove any `set-cookie` headers already in the response, including those added by other Cloudflare products such as Bot Management.
 
 <Render
 	file="troubleshoot-rules-with-trace"

src/content/docs/rules/transform/response-header-modification/reference/parameters.mdx

@@ -12,14 +12,15 @@ To set an HTTP response header, overwriting any headers with the same name, use
 
 - **operation**: `set`
 - Include one of the following parameters to define a static or dynamic value:
-
   - **value**: Specifies a static value for the HTTP response header.
   - **expression**: Specifies the expression that defines a value for the HTTP response header.
 
 To add an HTTP response header, keeping any existing headers with the same name, use the following parameters in the `action_parameters` field:
 
 - **operation**: `add`
-- **value**: Specifies a static value for the HTTP response header.
+- Include one of the following parameters to define a static or dynamic value:
+  - **value**: Specifies a static value for the HTTP response header.
+  - **expression**: Specifies the expression that defines a value for the HTTP response header.
 
 To remove an HTTP response header, set the following parameter in the `action_parameters` field:
 
@@ -48,7 +49,7 @@ The full syntax of the `action_parameters` field to define a dynamic HTTP respon
 "action_parameters": {
   "headers": {
     "<HEADER_NAME>": {
-      "operation": "set",
+      "operation": "<set|add>",
       "expression": "<EXPRESSION>"
     }
   }